Imaging

Osteoid osteoma (OO) is one of the most common benign tumors of bone, representing roughly 10% of all benign bone-forming tumors and 5% of all primary bone tumors.¹ The majority of cases occur in individuals under age 20 years and more frequently in males (2:1).² These lesions tend to be cortically based and most often located about the hip and in the diaphysis of long bones. They typically are characterized radiographically by a nidus less than 2 cm in diameter surrounded by dense, reactive bone of variable thickness.

The classic presentation of OO is localized, dull, aching pain that is worse at night and that is relieved with use of salicylates or other nonsteroidal anti-inflammatory drugs (NSAIDs).³ The diagnosis is made by patient history and plain radiographs, often supported by computed tomography (CT) or magnetic resonance imaging for appropriate identification of the tumor nidus. Despite effective pain relief with NSAIDs as well as evidence suggesting that the natural history of these tumors is self-limited, most patients forgo medical management in favor of elective surgical treatment.^4,5

Initially, treatment for OO focused on either symptom management or en bloc surgical resection of the tumor nidus. Several different minimally invasive therapies have since been developed, and good results reported.^6-8 More recently, use of percutaneous radiofrequency ablation (RFA) has increased, as this method has demonstrated high efficacy and minimal morbidity.^9-11 RFA for OO traditionally has been performed by radiologists under CT guidance in the radiology suite, but advances in intraoperative imaging techniques now allow orthopedic oncologists to perform image-guided RFA in the operating room.

To our knowledge, there have been no reports documenting use of intraoperative CT for localization of OO and use of RFA in the treatment of this lesion. In this article, we report the results of a series of 28 patients with OO treated with intraoperative CT-guided RFA by a single surgeon. We also provide a brief description of this novel technique.

Materials and Methods

The protocol used was approved by our institutional review board. All patients and/or their legal guardians provided informed consent to participate in the study and were informed at the time consent was obtained that case-related data would be submitted for publication.

Patients

Between September 2004 and December 2008, 28 patients (19 males, 9 females) with OO underwent intraoperative percutaneous image-guided RFA at a university hospital. Mean age was 19.5 years, median age was 16 years (range, 7-54 years). Patients were referred for RFA if they had clinical and radiographic features of OO (Figures 1, 2) and wanted to forgo continued medical management. As we selected only patients with lesions that we thought were amenable to percutaneous RFA—lesions involving the long and short bones of the upper or lower extremity and selected flat bones—en bloc surgical resection was not offered to these patients. Lesions were located in the upper extremity (n = 1), lower extremity (n = 24), and pelvis (n = 3) (Figure 3). Twenty-seven procedures were performed for initial tumor treatment and 1 for recurrence after previous open excision. Two additional procedures were later performed on separate patients with recurrent symptoms after the index procedure. All procedures were performed by the senior author (DML).

Procedure

With each patient, all options were discussed, including continued medical management versus surgical treatment, and informed consent was obtained. All procedures were performed with the patient under general anesthesia in the operating room. RFA for an upper extremity lesion was performed with the patient in the supine position with the ipsilateral extremity draped over a hand table. The 2 procedures for lesions in the talus or calcaneus were performed with the patient in the supine position using a standard table with the bottom of the table flexed down 90° to allow the nonaffected leg to hang over the end of the table. The affected extremity in each case was then positioned in a well-padded leg holder to allow the foot and ankle to be draped free for 360° imaging.

All other procedures for lower extremity diaphyseal or pelvic lesions were performed with a fracture table. After successful induction of general anesthesia, the patient was positioned supine on the table with the contralateral lower extremity abducted and externally rotated in a well-leg holder. The ipsilateral leg was held in the traction apparatus without traction applied and was prepared and draped accordingly (Figure 4). With use of the Siemens Siremobil ISO-C3D fluoroscopic C-arm (Siemens Medical Solutions, Malvern, Pennsylvania), a radiograph was taken of the affected area to identify the lesion. Local anesthetic was infiltrated into the surgical site down to the periosteum. A stab incision was made, and, with fluoroscopic guidance, a 0.062-mm Kirschner wire (K-wire) was placed into the lesion. Location within the tumor nidus was confirmed with biplanar fluoroscopic imaging. A Bonopty cannula (AprioMed, Uppsala, Sweden) was then passed over the K-wire. After the wire was removed, a 5-mm radiofrequency probe (Radionics, Burlington, Massachusetts) was placed through the cannula, and positioning within the nidus was confirmed with 3-dimensional (3-D) CT reconstructions in the sagittal, coronal, and axial planes (Figure 5). A radiofrequency generator (Radionics) was used to heat the lesion at 93°C for 7 minutes. The probe and trocar were then removed. Steri-strips and a sterile dressing were used to cover the wound, and the patient was taken to the recovery area after extubation. All patients were discharged home the day of the procedure.

Follow-Up

We phoned all the patients to ask about symptom recurrence, outside treatment, and satisfaction with RFA and to obtain informed consent to participate in our study. Only 1 of the 28 patients could not be reached and was lost to follow-up. Mean follow-up at time of study completion was 31.1 months (range, 5.2-55.8 months).

The 27 patients were asked a series of questions about their treatment: Have you had any recurrence of symptoms following treatment for your OO? Have you received treatment elsewhere? Were you satisfied with your treatment? Would you have the procedure again if you had a recurrence of symptoms?

Primary success was defined as complete pain relief after initial RFA with no evidence of recurrence at time of final follow-up, and secondary success was defined as presence of recurrent symptoms after initial RFA with complete pain relief after a second procedure with no evidence of recurrence.

Results

All RFAs were technically successful with adequate localization of the tumor nidus and subsequent probe placement within the lesion. There were no intraoperative or postoperative complications. All 28 patients were discharged home the day of procedure. Twenty-six patients (92.8%) experienced complete pain relief after primary RFA, had no evidence of recurrence at final follow-up, and denied symptom recurrence at time of study completion.

The other 2 patients reported symptom recurrence after the index treatment (1 proximal femur lesion, 1 distal femur lesion). One of these patients did well initially but had a recurrence about 2 months after the primary RFA; a second RFA provided complete resolution of pain with no evidence of recurrence at time of study completion. In the other patient’s case, intermittent pain persisted for 2 weeks after the primary RFA, and evidence of recurrence was documented 3 months after surgery; a second RFA was performed shortly thereafter, but the patient was subsequently lost to follow-up.

At time of study completion, all 27 patients who had been contacted by phone denied seeking additional treatment elsewhere and stated they would have the procedure again if their symptoms ever recurred.

Discussion

Osteoid osteoma is one of the most common benign tumors of bone. Over the past 2 decades, percutaneous RFA, in comparison with open excision, has emerged as a safe and effective treatment option with minimal patient morbidity.^9-11 RFA traditionally has been performed by radiologists under CT guidance in the radiology suite. However, now orthopedic surgeons can obtain advanced intraoperative imaging beyond standard fluoroscopy. The Siemens Siremobil ISO-C3D fluoroscopic C-arm is an innovative intraoperative imaging device that functions as a standard fluoroscope but also generates 3-D reconstructions of surgical anatomy. The isocentric design and integrated motor unit allow the C-arm to move through a 190º arc while centering its beam directly on the area of interest. This data set is transferred to a computer workstation, where it is reformatted so that CT-quality images are generated in axial, sagittal, and coronal planes. This acquisition process takes only minutes, and the multiplanar images produced may be simultaneously displayed and manipulated on the screen in real time.

One concern about this technology is the amount of radiation exposure for patients, surgeons, and operating room staff. The device measures only radiation time, and the amount of exposure during that time depends on the volume and density of the radiated body. We did not calculate the amount of exposure for this study. Mean exposure time was between 20 and 40 seconds, reflecting the number of attempts required to localize the lesion and the surgeon’s experience with the technique. Although the potential for increased exposure is a valid concern, previous studies using this technology have demonstrated that a similar average exposure time is equivalent to that of standard CT, and that use of the device, over conventional techniques, potentially can lead to decreased overall radiation exposure.^12,13

This series demonstrated that OO can be safely and effectively treated with intraoperative percutaneous RFA by an orthopedic oncologist. Our success rate is very similar to rates reported in the radiology literature. Studies are needed to confirm the efficacy of this novel technique in comparison with what has been reported in that literature. Given these promising preliminary results, and the relative ease of use and minimal learning curve associated with this technology, all orthopedic oncologists should be able to offer this treatment for OO. Furthermore, this technique allows orthopedic oncologists to provide appropriate definitive treatment and care directly, rather than by referring patients to radiologists.

In the treatment of OO, we reserve RFA for lesions involving the long and short bones of the upper and lower extremities, as well as selected flat bones, such as those in the pelvis. Although percutaneous RFA of spinal lesions has been reported in the literature, we think these represent a relative contraindication for this technique; image resolution, in our opinion, is not high enough to justify risking injury to the nerves in the spinal canal, lateral recesses, and neural foramina. In addition, given the radiation exposure, we recommend caution when using this technique for a pelvic or proximal femoral lesion in a woman of childbearing age.

Osteoid osteoma (OO) is one of the most common benign tumors of bone, representing roughly 10% of all benign bone-forming tumors and 5% of all primary bone tumors.¹ The majority of cases occur in individuals under age 20 years and more frequently in males (2:1).² These lesions tend to be cortically based and most often located about the hip and in the diaphysis of long bones. They typically are characterized radiographically by a nidus less than 2 cm in diameter surrounded by dense, reactive bone of variable thickness.

The classic presentation of OO is localized, dull, aching pain that is worse at night and that is relieved with use of salicylates or other nonsteroidal anti-inflammatory drugs (NSAIDs).³ The diagnosis is made by patient history and plain radiographs, often supported by computed tomography (CT) or magnetic resonance imaging for appropriate identification of the tumor nidus. Despite effective pain relief with NSAIDs as well as evidence suggesting that the natural history of these tumors is self-limited, most patients forgo medical management in favor of elective surgical treatment.^4,5

Initially, treatment for OO focused on either symptom management or en bloc surgical resection of the tumor nidus. Several different minimally invasive therapies have since been developed, and good results reported.^6-8 More recently, use of percutaneous radiofrequency ablation (RFA) has increased, as this method has demonstrated high efficacy and minimal morbidity.^9-11 RFA for OO traditionally has been performed by radiologists under CT guidance in the radiology suite, but advances in intraoperative imaging techniques now allow orthopedic oncologists to perform image-guided RFA in the operating room.

To our knowledge, there have been no reports documenting use of intraoperative CT for localization of OO and use of RFA in the treatment of this lesion. In this article, we report the results of a series of 28 patients with OO treated with intraoperative CT-guided RFA by a single surgeon. We also provide a brief description of this novel technique.

Materials and Methods

The protocol used was approved by our institutional review board. All patients and/or their legal guardians provided informed consent to participate in the study and were informed at the time consent was obtained that case-related data would be submitted for publication.

Patients

Between September 2004 and December 2008, 28 patients (19 males, 9 females) with OO underwent intraoperative percutaneous image-guided RFA at a university hospital. Mean age was 19.5 years, median age was 16 years (range, 7-54 years). Patients were referred for RFA if they had clinical and radiographic features of OO (Figures 1, 2) and wanted to forgo continued medical management. As we selected only patients with lesions that we thought were amenable to percutaneous RFA—lesions involving the long and short bones of the upper or lower extremity and selected flat bones—en bloc surgical resection was not offered to these patients. Lesions were located in the upper extremity (n = 1), lower extremity (n = 24), and pelvis (n = 3) (Figure 3). Twenty-seven procedures were performed for initial tumor treatment and 1 for recurrence after previous open excision. Two additional procedures were later performed on separate patients with recurrent symptoms after the index procedure. All procedures were performed by the senior author (DML).

Procedure

With each patient, all options were discussed, including continued medical management versus surgical treatment, and informed consent was obtained. All procedures were performed with the patient under general anesthesia in the operating room. RFA for an upper extremity lesion was performed with the patient in the supine position with the ipsilateral extremity draped over a hand table. The 2 procedures for lesions in the talus or calcaneus were performed with the patient in the supine position using a standard table with the bottom of the table flexed down 90° to allow the nonaffected leg to hang over the end of the table. The affected extremity in each case was then positioned in a well-padded leg holder to allow the foot and ankle to be draped free for 360° imaging.

All other procedures for lower extremity diaphyseal or pelvic lesions were performed with a fracture table. After successful induction of general anesthesia, the patient was positioned supine on the table with the contralateral lower extremity abducted and externally rotated in a well-leg holder. The ipsilateral leg was held in the traction apparatus without traction applied and was prepared and draped accordingly (Figure 4). With use of the Siemens Siremobil ISO-C3D fluoroscopic C-arm (Siemens Medical Solutions, Malvern, Pennsylvania), a radiograph was taken of the affected area to identify the lesion. Local anesthetic was infiltrated into the surgical site down to the periosteum. A stab incision was made, and, with fluoroscopic guidance, a 0.062-mm Kirschner wire (K-wire) was placed into the lesion. Location within the tumor nidus was confirmed with biplanar fluoroscopic imaging. A Bonopty cannula (AprioMed, Uppsala, Sweden) was then passed over the K-wire. After the wire was removed, a 5-mm radiofrequency probe (Radionics, Burlington, Massachusetts) was placed through the cannula, and positioning within the nidus was confirmed with 3-dimensional (3-D) CT reconstructions in the sagittal, coronal, and axial planes (Figure 5). A radiofrequency generator (Radionics) was used to heat the lesion at 93°C for 7 minutes. The probe and trocar were then removed. Steri-strips and a sterile dressing were used to cover the wound, and the patient was taken to the recovery area after extubation. All patients were discharged home the day of the procedure.

Follow-Up

We phoned all the patients to ask about symptom recurrence, outside treatment, and satisfaction with RFA and to obtain informed consent to participate in our study. Only 1 of the 28 patients could not be reached and was lost to follow-up. Mean follow-up at time of study completion was 31.1 months (range, 5.2-55.8 months).

The 27 patients were asked a series of questions about their treatment: Have you had any recurrence of symptoms following treatment for your OO? Have you received treatment elsewhere? Were you satisfied with your treatment? Would you have the procedure again if you had a recurrence of symptoms?

Primary success was defined as complete pain relief after initial RFA with no evidence of recurrence at time of final follow-up, and secondary success was defined as presence of recurrent symptoms after initial RFA with complete pain relief after a second procedure with no evidence of recurrence.

Results

All RFAs were technically successful with adequate localization of the tumor nidus and subsequent probe placement within the lesion. There were no intraoperative or postoperative complications. All 28 patients were discharged home the day of procedure. Twenty-six patients (92.8%) experienced complete pain relief after primary RFA, had no evidence of recurrence at final follow-up, and denied symptom recurrence at time of study completion.

The other 2 patients reported symptom recurrence after the index treatment (1 proximal femur lesion, 1 distal femur lesion). One of these patients did well initially but had a recurrence about 2 months after the primary RFA; a second RFA provided complete resolution of pain with no evidence of recurrence at time of study completion. In the other patient’s case, intermittent pain persisted for 2 weeks after the primary RFA, and evidence of recurrence was documented 3 months after surgery; a second RFA was performed shortly thereafter, but the patient was subsequently lost to follow-up.

At time of study completion, all 27 patients who had been contacted by phone denied seeking additional treatment elsewhere and stated they would have the procedure again if their symptoms ever recurred.

Discussion

Osteoid osteoma is one of the most common benign tumors of bone. Over the past 2 decades, percutaneous RFA, in comparison with open excision, has emerged as a safe and effective treatment option with minimal patient morbidity.^9-11 RFA traditionally has been performed by radiologists under CT guidance in the radiology suite. However, now orthopedic surgeons can obtain advanced intraoperative imaging beyond standard fluoroscopy. The Siemens Siremobil ISO-C3D fluoroscopic C-arm is an innovative intraoperative imaging device that functions as a standard fluoroscope but also generates 3-D reconstructions of surgical anatomy. The isocentric design and integrated motor unit allow the C-arm to move through a 190º arc while centering its beam directly on the area of interest. This data set is transferred to a computer workstation, where it is reformatted so that CT-quality images are generated in axial, sagittal, and coronal planes. This acquisition process takes only minutes, and the multiplanar images produced may be simultaneously displayed and manipulated on the screen in real time.

One concern about this technology is the amount of radiation exposure for patients, surgeons, and operating room staff. The device measures only radiation time, and the amount of exposure during that time depends on the volume and density of the radiated body. We did not calculate the amount of exposure for this study. Mean exposure time was between 20 and 40 seconds, reflecting the number of attempts required to localize the lesion and the surgeon’s experience with the technique. Although the potential for increased exposure is a valid concern, previous studies using this technology have demonstrated that a similar average exposure time is equivalent to that of standard CT, and that use of the device, over conventional techniques, potentially can lead to decreased overall radiation exposure.^12,13

This series demonstrated that OO can be safely and effectively treated with intraoperative percutaneous RFA by an orthopedic oncologist. Our success rate is very similar to rates reported in the radiology literature. Studies are needed to confirm the efficacy of this novel technique in comparison with what has been reported in that literature. Given these promising preliminary results, and the relative ease of use and minimal learning curve associated with this technology, all orthopedic oncologists should be able to offer this treatment for OO. Furthermore, this technique allows orthopedic oncologists to provide appropriate definitive treatment and care directly, rather than by referring patients to radiologists.

In the treatment of OO, we reserve RFA for lesions involving the long and short bones of the upper and lower extremities, as well as selected flat bones, such as those in the pelvis. Although percutaneous RFA of spinal lesions has been reported in the literature, we think these represent a relative contraindication for this technique; image resolution, in our opinion, is not high enough to justify risking injury to the nerves in the spinal canal, lateral recesses, and neural foramina. In addition, given the radiation exposure, we recommend caution when using this technique for a pelvic or proximal femoral lesion in a woman of childbearing age.

Osteoid osteoma (OO) is one of the most common benign tumors of bone, representing roughly 10% of all benign bone-forming tumors and 5% of all primary bone tumors.¹ The majority of cases occur in individuals under age 20 years and more frequently in males (2:1).² These lesions tend to be cortically based and most often located about the hip and in the diaphysis of long bones. They typically are characterized radiographically by a nidus less than 2 cm in diameter surrounded by dense, reactive bone of variable thickness.

The classic presentation of OO is localized, dull, aching pain that is worse at night and that is relieved with use of salicylates or other nonsteroidal anti-inflammatory drugs (NSAIDs).³ The diagnosis is made by patient history and plain radiographs, often supported by computed tomography (CT) or magnetic resonance imaging for appropriate identification of the tumor nidus. Despite effective pain relief with NSAIDs as well as evidence suggesting that the natural history of these tumors is self-limited, most patients forgo medical management in favor of elective surgical treatment.^4,5

Initially, treatment for OO focused on either symptom management or en bloc surgical resection of the tumor nidus. Several different minimally invasive therapies have since been developed, and good results reported.^6-8 More recently, use of percutaneous radiofrequency ablation (RFA) has increased, as this method has demonstrated high efficacy and minimal morbidity.^9-11 RFA for OO traditionally has been performed by radiologists under CT guidance in the radiology suite, but advances in intraoperative imaging techniques now allow orthopedic oncologists to perform image-guided RFA in the operating room.

To our knowledge, there have been no reports documenting use of intraoperative CT for localization of OO and use of RFA in the treatment of this lesion. In this article, we report the results of a series of 28 patients with OO treated with intraoperative CT-guided RFA by a single surgeon. We also provide a brief description of this novel technique.

Materials and Methods

The protocol used was approved by our institutional review board. All patients and/or their legal guardians provided informed consent to participate in the study and were informed at the time consent was obtained that case-related data would be submitted for publication.

Patients

Between September 2004 and December 2008, 28 patients (19 males, 9 females) with OO underwent intraoperative percutaneous image-guided RFA at a university hospital. Mean age was 19.5 years, median age was 16 years (range, 7-54 years). Patients were referred for RFA if they had clinical and radiographic features of OO (Figures 1, 2) and wanted to forgo continued medical management. As we selected only patients with lesions that we thought were amenable to percutaneous RFA—lesions involving the long and short bones of the upper or lower extremity and selected flat bones—en bloc surgical resection was not offered to these patients. Lesions were located in the upper extremity (n = 1), lower extremity (n = 24), and pelvis (n = 3) (Figure 3). Twenty-seven procedures were performed for initial tumor treatment and 1 for recurrence after previous open excision. Two additional procedures were later performed on separate patients with recurrent symptoms after the index procedure. All procedures were performed by the senior author (DML).

Procedure

With each patient, all options were discussed, including continued medical management versus surgical treatment, and informed consent was obtained. All procedures were performed with the patient under general anesthesia in the operating room. RFA for an upper extremity lesion was performed with the patient in the supine position with the ipsilateral extremity draped over a hand table. The 2 procedures for lesions in the talus or calcaneus were performed with the patient in the supine position using a standard table with the bottom of the table flexed down 90° to allow the nonaffected leg to hang over the end of the table. The affected extremity in each case was then positioned in a well-padded leg holder to allow the foot and ankle to be draped free for 360° imaging.

All other procedures for lower extremity diaphyseal or pelvic lesions were performed with a fracture table. After successful induction of general anesthesia, the patient was positioned supine on the table with the contralateral lower extremity abducted and externally rotated in a well-leg holder. The ipsilateral leg was held in the traction apparatus without traction applied and was prepared and draped accordingly (Figure 4). With use of the Siemens Siremobil ISO-C3D fluoroscopic C-arm (Siemens Medical Solutions, Malvern, Pennsylvania), a radiograph was taken of the affected area to identify the lesion. Local anesthetic was infiltrated into the surgical site down to the periosteum. A stab incision was made, and, with fluoroscopic guidance, a 0.062-mm Kirschner wire (K-wire) was placed into the lesion. Location within the tumor nidus was confirmed with biplanar fluoroscopic imaging. A Bonopty cannula (AprioMed, Uppsala, Sweden) was then passed over the K-wire. After the wire was removed, a 5-mm radiofrequency probe (Radionics, Burlington, Massachusetts) was placed through the cannula, and positioning within the nidus was confirmed with 3-dimensional (3-D) CT reconstructions in the sagittal, coronal, and axial planes (Figure 5). A radiofrequency generator (Radionics) was used to heat the lesion at 93°C for 7 minutes. The probe and trocar were then removed. Steri-strips and a sterile dressing were used to cover the wound, and the patient was taken to the recovery area after extubation. All patients were discharged home the day of the procedure.

Follow-Up

We phoned all the patients to ask about symptom recurrence, outside treatment, and satisfaction with RFA and to obtain informed consent to participate in our study. Only 1 of the 28 patients could not be reached and was lost to follow-up. Mean follow-up at time of study completion was 31.1 months (range, 5.2-55.8 months).

The 27 patients were asked a series of questions about their treatment: Have you had any recurrence of symptoms following treatment for your OO? Have you received treatment elsewhere? Were you satisfied with your treatment? Would you have the procedure again if you had a recurrence of symptoms?

Primary success was defined as complete pain relief after initial RFA with no evidence of recurrence at time of final follow-up, and secondary success was defined as presence of recurrent symptoms after initial RFA with complete pain relief after a second procedure with no evidence of recurrence.

Results

All RFAs were technically successful with adequate localization of the tumor nidus and subsequent probe placement within the lesion. There were no intraoperative or postoperative complications. All 28 patients were discharged home the day of procedure. Twenty-six patients (92.8%) experienced complete pain relief after primary RFA, had no evidence of recurrence at final follow-up, and denied symptom recurrence at time of study completion.

The other 2 patients reported symptom recurrence after the index treatment (1 proximal femur lesion, 1 distal femur lesion). One of these patients did well initially but had a recurrence about 2 months after the primary RFA; a second RFA provided complete resolution of pain with no evidence of recurrence at time of study completion. In the other patient’s case, intermittent pain persisted for 2 weeks after the primary RFA, and evidence of recurrence was documented 3 months after surgery; a second RFA was performed shortly thereafter, but the patient was subsequently lost to follow-up.

At time of study completion, all 27 patients who had been contacted by phone denied seeking additional treatment elsewhere and stated they would have the procedure again if their symptoms ever recurred.

Discussion

Osteoid osteoma is one of the most common benign tumors of bone. Over the past 2 decades, percutaneous RFA, in comparison with open excision, has emerged as a safe and effective treatment option with minimal patient morbidity.^9-11 RFA traditionally has been performed by radiologists under CT guidance in the radiology suite. However, now orthopedic surgeons can obtain advanced intraoperative imaging beyond standard fluoroscopy. The Siemens Siremobil ISO-C3D fluoroscopic C-arm is an innovative intraoperative imaging device that functions as a standard fluoroscope but also generates 3-D reconstructions of surgical anatomy. The isocentric design and integrated motor unit allow the C-arm to move through a 190º arc while centering its beam directly on the area of interest. This data set is transferred to a computer workstation, where it is reformatted so that CT-quality images are generated in axial, sagittal, and coronal planes. This acquisition process takes only minutes, and the multiplanar images produced may be simultaneously displayed and manipulated on the screen in real time.

One concern about this technology is the amount of radiation exposure for patients, surgeons, and operating room staff. The device measures only radiation time, and the amount of exposure during that time depends on the volume and density of the radiated body. We did not calculate the amount of exposure for this study. Mean exposure time was between 20 and 40 seconds, reflecting the number of attempts required to localize the lesion and the surgeon’s experience with the technique. Although the potential for increased exposure is a valid concern, previous studies using this technology have demonstrated that a similar average exposure time is equivalent to that of standard CT, and that use of the device, over conventional techniques, potentially can lead to decreased overall radiation exposure.^12,13

This series demonstrated that OO can be safely and effectively treated with intraoperative percutaneous RFA by an orthopedic oncologist. Our success rate is very similar to rates reported in the radiology literature. Studies are needed to confirm the efficacy of this novel technique in comparison with what has been reported in that literature. Given these promising preliminary results, and the relative ease of use and minimal learning curve associated with this technology, all orthopedic oncologists should be able to offer this treatment for OO. Furthermore, this technique allows orthopedic oncologists to provide appropriate definitive treatment and care directly, rather than by referring patients to radiologists.

In the treatment of OO, we reserve RFA for lesions involving the long and short bones of the upper and lower extremities, as well as selected flat bones, such as those in the pelvis. Although percutaneous RFA of spinal lesions has been reported in the literature, we think these represent a relative contraindication for this technique; image resolution, in our opinion, is not high enough to justify risking injury to the nerves in the spinal canal, lateral recesses, and neural foramina. In addition, given the radiation exposure, we recommend caution when using this technique for a pelvic or proximal femoral lesion in a woman of childbearing age.

Chronic plantar fasciitis is a major health care problem worldwide and affects nearly 10% of the US population. Plantar fasciitis presents as heel pain in the mornings and usually gets better and then gets worse. Inflammation at the plantar fascia attachment causes acute and sometimes disabling pain. Chronic pain at the site can develop as time goes on because of long-standing inflammatory changes. Fibrotic tissues may develop at the site. On a continuum, symptoms may begin in an insidious phase and progress to chronic pain. Although most cases resolve with conservative care, the numerous treatments for refractory plantar fasciitis attest to the lack of consensus regarding these cases. The condition frustrates patient and physician alike.

Treatments for refractory plantar fasciitis include conservative measures, including rest, analgesics, walking orthosis, heel cup, night splint, walking boot, and then, in a standard and logical progression, cortisone or platelet-rich plasma injections. Improved magnetic resonance imaging and ultrasonographic imaging allow accurate localization of the pathologic process,^1-3 and this localization in turn provides an opportunity to deliver a more reliable and focused intervention, as in needle-guided therapy.⁴ Surgical procedures for plantar fasciitis have included open or endoscopically assisted plantar fasciectomies with or without gastrocnemius recession; these procedures have had varying results. The emerging goals for this condition are a minimally invasive percutaneous intervention that is safe, effective, and well-tolerated and has minimal morbidity and a low complication rate.

We conducted a prospective study in which patients were allowed either to continue with noninvasive treatment or to undergo focal aspiration and partial fasciotomy with an ultrasonic probe. Study inclusion criteria were plantar fasciitis symptoms lasting 12 months or longer. Exclusion criteria were unwillingness to participate in the study. Prior treatments, even surgeries, were not exclusionary.

Twelve patients with refractory plantar fasciitis lasting a mean of 19 months (minimum, 12 months; range, 12-24 months) chose the procedure. They all had failed conservative care, including physical therapy, casting, shockwave therapy, and invasive procedures such as injections and endoscopic partial releases. Four of the 12 had undergone an open or endoscopic partial release at a different institution but had experienced no improvement in symptoms.

Based on the study protocol, patients continued noninvasive care (night splint, stretching exercises) for 2 to 6 weeks after the initial visit. When this conservative care failed, they were offered focal partial fasciectomy with a percutaneous ultrasonic probe. American Orthopaedic Foot and Ankle Society (AOFAS) scores were obtained before and after surgery. Follow-up consisted of clinic visits 2 weeks after surgery and monthly thereafter. I saw all 12 patients 3 months after surgery (range, 11-14 weeks), and all 12 underwent postoperative physical therapy.

Technique

The TX1 Tissue Removal System (Tenex Health, Lake Forest, California) (Figure 1) consists of an energy module, a pump/suction cassette that provides irrigation and suction through a probe, and the probe itself, the TX1, which is the size of an 18-gauge needle and delivers ultrasonic energy. The cassette is inserted into the energy module, and the ultrasonic energy probe is primed so it will deliver the irrigation fluid, normal saline. The safety features of the energy module are such that no energy is expended unless the system is properly irrigating and aspirating the diseased tissue. Ultrasonic treatment may be performed in a clinical or ambulatory surgical center. The patient is placed supine on an operating table, on a clinical examining table, or, if in a cast room, on a cart. A pillow is placed under the distal tibia so the knees can flex slightly, and the patient is positioned so the feet are free of the edge of the bed or gurney (Figure 2).

The pathology is first confirmed by ultrasonography (Figures 3–5). The first step is to identify the calcaneus with the sensor along the long axis of the foot. Then the plantar fascia is visualized and followed along its long axis to the site of attachment at the medial tubercle. As the pathologic process involves the medial site of attachment, a transverse image may also be obtained to better understand the medial/lateral extent of the disease process. The ultrasonographic image of plantar fasciitis has been well characterized.^2,5 The pathology is visualized as an area of edema or of disruption of the linear appearance of the fascia as it attaches to the calcaneus. While the diagnosis is being confirmed, the optimal site for probe insertion should be considered based on the location of the pain and the localization of the pathology by the 2 orthogonal images.

The area is prepared as if for an injection and is squared off with sterile towels. Then the sensor is placed in the sterile sleeve. The area of maximum tenderness is again confirmed. Determining the location of the probe insertion site is a crucial step. We use the ultrasonic sensor in the longitudinal and transverse planes to direct the injection of a fast-acting local anesthetic to the medial aspect of the calcaneus. A skin wheal is created, and the fast-acting local anesthetic (3-4 mL) is injected into the region of the fascia pathology.

An 11-blade knife is used to create a site for the probe through the skin wheal at the medial aspect of the heel, in line with the pathology (Figure 6). The probe is then introduced through the puncture site and is identified, along with the pathology, with the sensor, which may be oriented transverse or longitudinal to the long axis of the foot.

Once the pathologic area is identified, the ultrasonic energy is delivered to the region by the probe, which is activated with a foot pedal, effectively releasing the pathologic tissue from its insertion at the medial tubercle of the calcaneus. The probe is moved in a linear fashion medially and laterally within the lesion across the site of attachment. Treatment continues until the entire soft-tissue lesion is addressed.

Postoperative Care

The wound or wounds are closed with a nylon stitch and Steri-Strip (3M, St. Paul, Minnesota) and covered with Tegaderm (3M) or similar dressing (Figure 7). A compressive dressing is applied. The dressing is removed in 2 to 3 days; the Steri-Strip and stitch are removed in 10 to 14 days. A walking boot is put on immediately after the procedure (most patients in this study already have a boot) and is worn for a few days, or until the symptoms have resolved. How long the boot is used is very much based on patient preference. Patients may continue stretching exercises at home, but there should be no high-impact activity. As-needed ice and analgesics are recommended for the first few days.

The 12 patients had a mean preoperative AOFAS score of 30 (range, 17-46) and a mean postoperative score of 88 (range, 25-92). By the 3-month postoperative visit, symptoms were resolved in 11 patients (no activity restricted by plantar fascia pain). On physical examination, 11 patients had no palpable tenderness at the site of preoperative pain. Pain relief was documented as having occurred between 5 and 13 weeks after treatment. One patient had bilateral procedures. One foot was treated, pain resolved by the 3-month postoperative visit, and the patient asked for the other foot to be treated. Three months after the second procedure, he had minimal non-activity-restricting pain. There were no postoperative infections or wound complications.

I phoned my patients during postoperative month 24. All 12 patients (13 feet) indicated they were essentially pain-free. None admitted to activity restriction or required over-the-counter pain medication. All indicated they were satisfied with the procedure and would have it again.

The refractory nature of plantar fasciitis, and the resistance to and unpredictability of current treatment options, is well known. Considerable efforts have been made to develop treatment guidelines and algorithms.⁶ A standard and logical treatment plan involves initial attempts with rest, analgesics, and a walking orthosis and then, if those fail, cortisone or platelet-rich plasma injections. Reluctance to perform surgery is well justified because of the unpredictability of the intervention. As might be expected, the utility of ultrasonography has been on the rise. The diagnostic value of ultrasonography, first recognized in the early 1970s, is of increasing importance.^7,8 Subsequent use of ultrasonographic imaging as guidance for various treatments, including percutaneous release, has also been recognized and documented.^4,9-12 The present article is the first to describe and document the outcome of using ultrasonic energy for percutaneous release of the diseased attachment of the plantar fascia.

This report is preliminary and was designed to alert the orthopedic community to a safe and promising treatment for a chronic, refractory condition. The safety and efficacy of this treatment are reflected in our experience and have been documented for tennis elbow as well.¹³

This study was limited by its single-surgeon and relatively small clinical experience. Nevertheless, the benefits of this novel technique—effectiveness, safety, tolerability, and rapid recovery—are encouraging enough to share at this time. Prospective randomized controlled studies are needed.

Conclusion

This is the first report of a plantar fascia partial release guided by ultrasonic energy delivered by a percutaneously inserted probe under local anesthesia. The procedure appears to be a safe, effective, well-tolerated treatment for a condition that is refractory to other options. More studies are needed to further validate the safety and efficacy of this innovative treatment modality.

Chronic plantar fasciitis is a major health care problem worldwide and affects nearly 10% of the US population. Plantar fasciitis presents as heel pain in the mornings and usually gets better and then gets worse. Inflammation at the plantar fascia attachment causes acute and sometimes disabling pain. Chronic pain at the site can develop as time goes on because of long-standing inflammatory changes. Fibrotic tissues may develop at the site. On a continuum, symptoms may begin in an insidious phase and progress to chronic pain. Although most cases resolve with conservative care, the numerous treatments for refractory plantar fasciitis attest to the lack of consensus regarding these cases. The condition frustrates patient and physician alike.

Treatments for refractory plantar fasciitis include conservative measures, including rest, analgesics, walking orthosis, heel cup, night splint, walking boot, and then, in a standard and logical progression, cortisone or platelet-rich plasma injections. Improved magnetic resonance imaging and ultrasonographic imaging allow accurate localization of the pathologic process,^1-3 and this localization in turn provides an opportunity to deliver a more reliable and focused intervention, as in needle-guided therapy.⁴ Surgical procedures for plantar fasciitis have included open or endoscopically assisted plantar fasciectomies with or without gastrocnemius recession; these procedures have had varying results. The emerging goals for this condition are a minimally invasive percutaneous intervention that is safe, effective, and well-tolerated and has minimal morbidity and a low complication rate.

We conducted a prospective study in which patients were allowed either to continue with noninvasive treatment or to undergo focal aspiration and partial fasciotomy with an ultrasonic probe. Study inclusion criteria were plantar fasciitis symptoms lasting 12 months or longer. Exclusion criteria were unwillingness to participate in the study. Prior treatments, even surgeries, were not exclusionary.

Twelve patients with refractory plantar fasciitis lasting a mean of 19 months (minimum, 12 months; range, 12-24 months) chose the procedure. They all had failed conservative care, including physical therapy, casting, shockwave therapy, and invasive procedures such as injections and endoscopic partial releases. Four of the 12 had undergone an open or endoscopic partial release at a different institution but had experienced no improvement in symptoms.

Based on the study protocol, patients continued noninvasive care (night splint, stretching exercises) for 2 to 6 weeks after the initial visit. When this conservative care failed, they were offered focal partial fasciectomy with a percutaneous ultrasonic probe. American Orthopaedic Foot and Ankle Society (AOFAS) scores were obtained before and after surgery. Follow-up consisted of clinic visits 2 weeks after surgery and monthly thereafter. I saw all 12 patients 3 months after surgery (range, 11-14 weeks), and all 12 underwent postoperative physical therapy.

Technique

The TX1 Tissue Removal System (Tenex Health, Lake Forest, California) (Figure 1) consists of an energy module, a pump/suction cassette that provides irrigation and suction through a probe, and the probe itself, the TX1, which is the size of an 18-gauge needle and delivers ultrasonic energy. The cassette is inserted into the energy module, and the ultrasonic energy probe is primed so it will deliver the irrigation fluid, normal saline. The safety features of the energy module are such that no energy is expended unless the system is properly irrigating and aspirating the diseased tissue. Ultrasonic treatment may be performed in a clinical or ambulatory surgical center. The patient is placed supine on an operating table, on a clinical examining table, or, if in a cast room, on a cart. A pillow is placed under the distal tibia so the knees can flex slightly, and the patient is positioned so the feet are free of the edge of the bed or gurney (Figure 2).

The pathology is first confirmed by ultrasonography (Figures 3–5). The first step is to identify the calcaneus with the sensor along the long axis of the foot. Then the plantar fascia is visualized and followed along its long axis to the site of attachment at the medial tubercle. As the pathologic process involves the medial site of attachment, a transverse image may also be obtained to better understand the medial/lateral extent of the disease process. The ultrasonographic image of plantar fasciitis has been well characterized.^2,5 The pathology is visualized as an area of edema or of disruption of the linear appearance of the fascia as it attaches to the calcaneus. While the diagnosis is being confirmed, the optimal site for probe insertion should be considered based on the location of the pain and the localization of the pathology by the 2 orthogonal images.

The area is prepared as if for an injection and is squared off with sterile towels. Then the sensor is placed in the sterile sleeve. The area of maximum tenderness is again confirmed. Determining the location of the probe insertion site is a crucial step. We use the ultrasonic sensor in the longitudinal and transverse planes to direct the injection of a fast-acting local anesthetic to the medial aspect of the calcaneus. A skin wheal is created, and the fast-acting local anesthetic (3-4 mL) is injected into the region of the fascia pathology.

An 11-blade knife is used to create a site for the probe through the skin wheal at the medial aspect of the heel, in line with the pathology (Figure 6). The probe is then introduced through the puncture site and is identified, along with the pathology, with the sensor, which may be oriented transverse or longitudinal to the long axis of the foot.

Once the pathologic area is identified, the ultrasonic energy is delivered to the region by the probe, which is activated with a foot pedal, effectively releasing the pathologic tissue from its insertion at the medial tubercle of the calcaneus. The probe is moved in a linear fashion medially and laterally within the lesion across the site of attachment. Treatment continues until the entire soft-tissue lesion is addressed.

Postoperative Care

The wound or wounds are closed with a nylon stitch and Steri-Strip (3M, St. Paul, Minnesota) and covered with Tegaderm (3M) or similar dressing (Figure 7). A compressive dressing is applied. The dressing is removed in 2 to 3 days; the Steri-Strip and stitch are removed in 10 to 14 days. A walking boot is put on immediately after the procedure (most patients in this study already have a boot) and is worn for a few days, or until the symptoms have resolved. How long the boot is used is very much based on patient preference. Patients may continue stretching exercises at home, but there should be no high-impact activity. As-needed ice and analgesics are recommended for the first few days.

The 12 patients had a mean preoperative AOFAS score of 30 (range, 17-46) and a mean postoperative score of 88 (range, 25-92). By the 3-month postoperative visit, symptoms were resolved in 11 patients (no activity restricted by plantar fascia pain). On physical examination, 11 patients had no palpable tenderness at the site of preoperative pain. Pain relief was documented as having occurred between 5 and 13 weeks after treatment. One patient had bilateral procedures. One foot was treated, pain resolved by the 3-month postoperative visit, and the patient asked for the other foot to be treated. Three months after the second procedure, he had minimal non-activity-restricting pain. There were no postoperative infections or wound complications.

I phoned my patients during postoperative month 24. All 12 patients (13 feet) indicated they were essentially pain-free. None admitted to activity restriction or required over-the-counter pain medication. All indicated they were satisfied with the procedure and would have it again.

The refractory nature of plantar fasciitis, and the resistance to and unpredictability of current treatment options, is well known. Considerable efforts have been made to develop treatment guidelines and algorithms.⁶ A standard and logical treatment plan involves initial attempts with rest, analgesics, and a walking orthosis and then, if those fail, cortisone or platelet-rich plasma injections. Reluctance to perform surgery is well justified because of the unpredictability of the intervention. As might be expected, the utility of ultrasonography has been on the rise. The diagnostic value of ultrasonography, first recognized in the early 1970s, is of increasing importance.^7,8 Subsequent use of ultrasonographic imaging as guidance for various treatments, including percutaneous release, has also been recognized and documented.^4,9-12 The present article is the first to describe and document the outcome of using ultrasonic energy for percutaneous release of the diseased attachment of the plantar fascia.

This report is preliminary and was designed to alert the orthopedic community to a safe and promising treatment for a chronic, refractory condition. The safety and efficacy of this treatment are reflected in our experience and have been documented for tennis elbow as well.¹³

This study was limited by its single-surgeon and relatively small clinical experience. Nevertheless, the benefits of this novel technique—effectiveness, safety, tolerability, and rapid recovery—are encouraging enough to share at this time. Prospective randomized controlled studies are needed.

Conclusion

This is the first report of a plantar fascia partial release guided by ultrasonic energy delivered by a percutaneously inserted probe under local anesthesia. The procedure appears to be a safe, effective, well-tolerated treatment for a condition that is refractory to other options. More studies are needed to further validate the safety and efficacy of this innovative treatment modality.

Chronic plantar fasciitis is a major health care problem worldwide and affects nearly 10% of the US population. Plantar fasciitis presents as heel pain in the mornings and usually gets better and then gets worse. Inflammation at the plantar fascia attachment causes acute and sometimes disabling pain. Chronic pain at the site can develop as time goes on because of long-standing inflammatory changes. Fibrotic tissues may develop at the site. On a continuum, symptoms may begin in an insidious phase and progress to chronic pain. Although most cases resolve with conservative care, the numerous treatments for refractory plantar fasciitis attest to the lack of consensus regarding these cases. The condition frustrates patient and physician alike.

Treatments for refractory plantar fasciitis include conservative measures, including rest, analgesics, walking orthosis, heel cup, night splint, walking boot, and then, in a standard and logical progression, cortisone or platelet-rich plasma injections. Improved magnetic resonance imaging and ultrasonographic imaging allow accurate localization of the pathologic process,^1-3 and this localization in turn provides an opportunity to deliver a more reliable and focused intervention, as in needle-guided therapy.⁴ Surgical procedures for plantar fasciitis have included open or endoscopically assisted plantar fasciectomies with or without gastrocnemius recession; these procedures have had varying results. The emerging goals for this condition are a minimally invasive percutaneous intervention that is safe, effective, and well-tolerated and has minimal morbidity and a low complication rate.

We conducted a prospective study in which patients were allowed either to continue with noninvasive treatment or to undergo focal aspiration and partial fasciotomy with an ultrasonic probe. Study inclusion criteria were plantar fasciitis symptoms lasting 12 months or longer. Exclusion criteria were unwillingness to participate in the study. Prior treatments, even surgeries, were not exclusionary.

Twelve patients with refractory plantar fasciitis lasting a mean of 19 months (minimum, 12 months; range, 12-24 months) chose the procedure. They all had failed conservative care, including physical therapy, casting, shockwave therapy, and invasive procedures such as injections and endoscopic partial releases. Four of the 12 had undergone an open or endoscopic partial release at a different institution but had experienced no improvement in symptoms.

Based on the study protocol, patients continued noninvasive care (night splint, stretching exercises) for 2 to 6 weeks after the initial visit. When this conservative care failed, they were offered focal partial fasciectomy with a percutaneous ultrasonic probe. American Orthopaedic Foot and Ankle Society (AOFAS) scores were obtained before and after surgery. Follow-up consisted of clinic visits 2 weeks after surgery and monthly thereafter. I saw all 12 patients 3 months after surgery (range, 11-14 weeks), and all 12 underwent postoperative physical therapy.

Technique

The TX1 Tissue Removal System (Tenex Health, Lake Forest, California) (Figure 1) consists of an energy module, a pump/suction cassette that provides irrigation and suction through a probe, and the probe itself, the TX1, which is the size of an 18-gauge needle and delivers ultrasonic energy. The cassette is inserted into the energy module, and the ultrasonic energy probe is primed so it will deliver the irrigation fluid, normal saline. The safety features of the energy module are such that no energy is expended unless the system is properly irrigating and aspirating the diseased tissue. Ultrasonic treatment may be performed in a clinical or ambulatory surgical center. The patient is placed supine on an operating table, on a clinical examining table, or, if in a cast room, on a cart. A pillow is placed under the distal tibia so the knees can flex slightly, and the patient is positioned so the feet are free of the edge of the bed or gurney (Figure 2).

The pathology is first confirmed by ultrasonography (Figures 3–5). The first step is to identify the calcaneus with the sensor along the long axis of the foot. Then the plantar fascia is visualized and followed along its long axis to the site of attachment at the medial tubercle. As the pathologic process involves the medial site of attachment, a transverse image may also be obtained to better understand the medial/lateral extent of the disease process. The ultrasonographic image of plantar fasciitis has been well characterized.^2,5 The pathology is visualized as an area of edema or of disruption of the linear appearance of the fascia as it attaches to the calcaneus. While the diagnosis is being confirmed, the optimal site for probe insertion should be considered based on the location of the pain and the localization of the pathology by the 2 orthogonal images.

The area is prepared as if for an injection and is squared off with sterile towels. Then the sensor is placed in the sterile sleeve. The area of maximum tenderness is again confirmed. Determining the location of the probe insertion site is a crucial step. We use the ultrasonic sensor in the longitudinal and transverse planes to direct the injection of a fast-acting local anesthetic to the medial aspect of the calcaneus. A skin wheal is created, and the fast-acting local anesthetic (3-4 mL) is injected into the region of the fascia pathology.

An 11-blade knife is used to create a site for the probe through the skin wheal at the medial aspect of the heel, in line with the pathology (Figure 6). The probe is then introduced through the puncture site and is identified, along with the pathology, with the sensor, which may be oriented transverse or longitudinal to the long axis of the foot.

Once the pathologic area is identified, the ultrasonic energy is delivered to the region by the probe, which is activated with a foot pedal, effectively releasing the pathologic tissue from its insertion at the medial tubercle of the calcaneus. The probe is moved in a linear fashion medially and laterally within the lesion across the site of attachment. Treatment continues until the entire soft-tissue lesion is addressed.

Postoperative Care

The wound or wounds are closed with a nylon stitch and Steri-Strip (3M, St. Paul, Minnesota) and covered with Tegaderm (3M) or similar dressing (Figure 7). A compressive dressing is applied. The dressing is removed in 2 to 3 days; the Steri-Strip and stitch are removed in 10 to 14 days. A walking boot is put on immediately after the procedure (most patients in this study already have a boot) and is worn for a few days, or until the symptoms have resolved. How long the boot is used is very much based on patient preference. Patients may continue stretching exercises at home, but there should be no high-impact activity. As-needed ice and analgesics are recommended for the first few days.

The 12 patients had a mean preoperative AOFAS score of 30 (range, 17-46) and a mean postoperative score of 88 (range, 25-92). By the 3-month postoperative visit, symptoms were resolved in 11 patients (no activity restricted by plantar fascia pain). On physical examination, 11 patients had no palpable tenderness at the site of preoperative pain. Pain relief was documented as having occurred between 5 and 13 weeks after treatment. One patient had bilateral procedures. One foot was treated, pain resolved by the 3-month postoperative visit, and the patient asked for the other foot to be treated. Three months after the second procedure, he had minimal non-activity-restricting pain. There were no postoperative infections or wound complications.

I phoned my patients during postoperative month 24. All 12 patients (13 feet) indicated they were essentially pain-free. None admitted to activity restriction or required over-the-counter pain medication. All indicated they were satisfied with the procedure and would have it again.

The refractory nature of plantar fasciitis, and the resistance to and unpredictability of current treatment options, is well known. Considerable efforts have been made to develop treatment guidelines and algorithms.⁶ A standard and logical treatment plan involves initial attempts with rest, analgesics, and a walking orthosis and then, if those fail, cortisone or platelet-rich plasma injections. Reluctance to perform surgery is well justified because of the unpredictability of the intervention. As might be expected, the utility of ultrasonography has been on the rise. The diagnostic value of ultrasonography, first recognized in the early 1970s, is of increasing importance.^7,8 Subsequent use of ultrasonographic imaging as guidance for various treatments, including percutaneous release, has also been recognized and documented.^4,9-12 The present article is the first to describe and document the outcome of using ultrasonic energy for percutaneous release of the diseased attachment of the plantar fascia.

This report is preliminary and was designed to alert the orthopedic community to a safe and promising treatment for a chronic, refractory condition. The safety and efficacy of this treatment are reflected in our experience and have been documented for tennis elbow as well.¹³

This study was limited by its single-surgeon and relatively small clinical experience. Nevertheless, the benefits of this novel technique—effectiveness, safety, tolerability, and rapid recovery—are encouraging enough to share at this time. Prospective randomized controlled studies are needed.

Conclusion

This is the first report of a plantar fascia partial release guided by ultrasonic energy delivered by a percutaneously inserted probe under local anesthesia. The procedure appears to be a safe, effective, well-tolerated treatment for a condition that is refractory to other options. More studies are needed to further validate the safety and efficacy of this innovative treatment modality.

Air-filled pulmonary lesions commonly detected on chest computed tomography. Cystic lung lesions should be distinguished from other air-filled lesions to facilitate diagnosis. Primary care physicians play an integral role in the recognition of cystic lung disease.

The differential diagnosis of cystic lung disease is broad and includes isolated pulmonary, systemic, infectious, and congenital etiologies.

Here, we aim to provide a systematic, stepwise approach to help differentiate among the various cystic lung diseases and devise an algorithm for diagnosis. In doing so, we will discuss the clinical and radiographic features of many of these diseases:

• Lymphangioleiomyomatosis
• Birt-Hogg-Dubé syndrome
• Pulmonary Langerhans cell histiocytosis
• Interstitial pneumonia (desquamative interstitial pneumonia, lymphocytic interstitial pneumonia)
• Congenital cystic lung disease (congenital pulmonary airway malformation, pulmonary sequestration, bronchogenic cyst) Pulmonary infection
• Systemic disease (amyloidosis, light chain deposition disease, neurofibromatosis type 1).

STEP 1: RULE OUT CYST-MIMICS

A pulmonary cyst is a round, circumscribed space surrounded by an epithelial or fibrous wall of variable thickness.¹ On chest radiography and computed tomography, a cyst appears as a round parenchymal lucency or low-attenuating area with a well-defined interface with normal lung.¹ Cysts vary in wall thickness but  usually have a thin wall (< 2 mm) and occur without associated pulmonary emphysema.¹ They typically contain air but occasionally contain fluid or solid material.

A pulmonary cyst can be categorized as a bulla, bleb, or pneumatocele.

Pulmonary cysts can be categorized as bullae, blebs, or pneumatoceles

Bullae are larger than 1 cm in diameter, sharply demarcated by a thin wall, and usually accompanied by emphysematous changes in the adjacent lung.¹

Blebs are no larger than 1 cm in diameter, are located within the visceral pleura or the subpleural space, and appear on computed tomography as thin-walled air spaces that are contiguous with the pleura.¹ The distinction between a bleb and a bulla is of little clinical importance, and is often unnecessary.

Pneumatoceles are cysts that are frequently caused by acute pneumonia, trauma, or aspiration of hydrocarbon fluid, and are usually transient.¹

Mimics of pulmonary cysts include pulmonary cavities, emphysema, loculated pneumothoraces, honeycomb lung, and bronchiectasis (Figure 1).²

Pulmonary cavities differ from cysts in that their walls are typically thicker (usually > 4 mm).³

Emphysema differs from cystic lung disease as it typically leads to focal areas or regions of decreased lung attenuation that do not have defined walls.¹

Honeycombing refers to a cluster or row of cysts, 1 to 3 mm in wall thickness and typically 3 to 10 mm in diameter, that are associated with end-stage lung fibrosis.¹ They are typically subpleural in distribution and are accompanied by fibrotic features such as reticulation and traction bronchiectasis.¹

Bronchiectasis is dilation and distortion of bronchi and bronchioles and can be mistaken for cysts when viewed en face.¹

Loculated pneumothoraces can also mimic pulmonary cysts, but they typically fail to adhere to a defined anatomic unit and are subpleural in distribution.

STEP 2: CHARACTERIZE THE CLINICAL PRESENTATION

Clinical signs and symptoms of cystic lung disease play a key role in diagnosis (Table 1). For instance, spontaneous pneumothorax is commonly associated with diffuse cystic lung disease (lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome), while insidious dyspnea, with or without associated pneumothorax, is usually associated with the interstitial pneumonias (lymphocytic interstitial pneumonia and desquamative interstitial pneumonia).

In addition, congenital abnormalities of the lung can lead to cyst formation. These abnormalities, especially when associated with other congenital abnormalities, are often diagnosed in the prenatal and perinatal periods. However, some remain undetected until incidentally found later in adulthood or if superimposing infection develops.

Primary pulmonary infections can also cause parenchymal necrosis, which in turn cavitates or forms cysts.⁴

Lastly, cystic lung diseases can occur as part of a multiorgan or systemic illness in which the lung is one of the organs involved. Although usually diagnosed before the discovery of cysts or manifestations of pulmonary symptoms, they can present as a diagnostic challenge, especially when lung cysts are the initial presentation.bsence of amyloid fibrils.

In view of the features of the different types of cystic lung disease, adults with cystic lung disease can be grouped according to their typical clinical presentations (Table 2):

• Insidious dyspnea or spontaneous pneumothorax
• Incidentally found cysts or recurrent pneumonia
• Signs and symptoms of primary pulmonary infection
• Signs and symptoms that are primarily nonpulmonary.

Insidious dyspnea or spontaneous pneumothorax

Insidious dyspnea or spontaneous pneumothorax can be manifestations of lymphangioleiomyomatosis, Birt-Hogg-Dubé syndrome, pulmonary Langerhans cell histiocytosis, desquamative interstitial pneumonia, or lymphocytic interstitial pneumonia.

Lymphangioleiomyomatosis is characterized by abnormal cellular proliferation within the lung, kidney, lymphatic system, or any combination.⁵ The peak prevalence is in the third to fourth decades of life, and most patients are women of childbearing age.⁶ In addition to progressive dyspnea on exertion and pneumothorax, other signs and symptoms include hemoptysis, nonproductive cough, chylous pleural effusion, and ascites.^7,8

Birt-Hogg-Dubé syndrome is caused by germline mutations in the folliculin (FLCN) gene.⁹ It is characterized by skin fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and renal cancer.¹⁰

Pulmonary Langerhans cell histiocytosis is part of the spectrum of Langerhans cell histiocytosis that, in addition to the lungs, can also involve the bone, pituitary gland, thyroid, skin, lymph nodes, and liver.¹¹ It occurs almost exclusively in smokers, affecting individuals in their 20s and 30s, with no gender predilection.^12,13 In addition to nonproductive cough and dyspnea, patients can also present with fever, anorexia, and weight loss,¹³ but approximately 25% of patients are asymptomatic.¹⁴

Desquamative interstitial pneumonia is an idiopathic interstitial pneumonia that, like pulmonary Langerhans cell histiocytosis, is seen almost exclusively in current or former smokers, who account for about 90% of patients with this disease. It affects almost twice as many men as women.^15,16 The mean age at onset is 42 to 46.^15,16 In addition to insidious cough and dyspnea, digital clubbing develops in 26% to 40% of patients.^16,17

Lymphocytic interstitial pneumonia is another rare idiopathic pneumonia, usually associated with connective tissue disease, Sjögren syndrome, immunodeficiencies, and viral infections.^18­–21 It is more common in women, presenting between the 4th and 7th decades of life, with a mean age at diagnosis of 50 to 56.^18,22 In addition to progressive dyspnea and cough, other symptoms include weight loss, pleuritic pain, arthralgias, fatigue, night sweats, and fever.²³

In summary, in this clinical group, lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome should be considered when patients present with spontaneous pneumothorax; those with Birt-Hogg-Dubé syndrome also present with skin lesions or renal cancer. In patients with progressive dyspnea and cough, lymphocytic interstitial pneumonia should be considered in those with a known history of connective tissue disease or immunodeficiency. Pulmonary Langerhans cell histiocytosis typically presents at a younger age (20 to 30 years old) than desquamative interstitial pneumonia (smokers in their 40s). Making the distinction, however, will likely require imaging with computed tomography.

Incidentally found cysts or recurrent pneumonia

Incidentally found cysts or recurrent pneumonia can be manifestations of congenital pulmonary airway malformation, pulmonary sequestration, or bronchogenic cyst.

Congenital pulmonary airway malformation, of which there are five types, is the most common pulmonary congenital abnormality. It accounts for up to 95% of cases of congenital cystic lung disease.^24,25 About 85% of cases are detected in the prenatal or perinatal periods.²⁶ Late-onset congenital pulmonary airway malformation (arising in childhood to adulthood) presents with recurrent pneumonia in about 75% of cases and can be misdiagnosed as lung abscess, pulmonary tuberculosis, or bronchiectasis.²⁷

Pulmonary sequestration, the second most common pulmonary congenital abnormality, is characterized by a portion of lung that does not connect to the tracheobronchial tree and has its own systemic arterial supply.²⁴ Intralobar sequestration, which shares the pleural investment with normal lung, accounts for about 80% of cases of pulmonary sequestration.^28–30 In addition to signs or symptoms of pulmonary infection, patients with pulmonary sequestration can remain asymp-
tomatic (about 25% of cases), or can present with hemoptysis or hemothorax.^28–30 In adults, the typical age at presentation is between 20 and 25.^29,30

Bronchogenic cyst is usually life-threatening in children. In adults, it commonly causes cough and chest pain.³¹ Hemoptysis, dysphagia, hoarseness, and diaphragmatic paralysis can also occur.^32,33 The mean age at diagnosis in adults is 35 to 40.^31,32

In summary, most cases of recurrent pneumonia with cysts are due to congenital pulmonary airway malformation. Pulmonary sequestration is the second most common cause of cystic lung disease in this group. Bronchogenic cyst is usually fatal in fetal development; smaller cysts can go unnoticed during the earlier years and are later found incidentally as imaging abnormalities in adults.

Signs and symptoms of primary pulmonary infections

Signs and symptoms of primary pulmonary infections can be due to Pneumocystis jirovecii pneumonia or echinococcal infections.

P jirovecii pneumonia commonly develops in patients with human immunodeficiency virus infection and low CD4 counts, recipients of hematologic or solid-organ transplants, and those receiving immunosuppressive therapy (eg, glucocorticoids or chemotherapy).

Echinococcal infections (with Echinococcus granulosus or multilocularis species) are more common in less-developed countries such as those in South America or the Middle East, in China, or in patients who have traveled to endemic areas.³⁴

In summary, cystic lung disease in patients with primary pulmonary infections can be diagnosed by the patient’s clinical history and risk factors for infections. Those with human immunodeficiency virus infection and other causes of immunodeficiency are predisposed to P jirovecii pneumonia. Echinococcal infections occur in those with a history of travel to an endemic area.

Primarily nonpulmonary signs and symptoms

If the patient has primarily nonpulmonary signs and symptoms, think about pulmonary amyloidosis, light chain deposition disease, and neurofibromatosis type 1.

Pulmonary amyloidosis has a variety of manifestations, including tracheobronchial disease, nodular parenchymal disease, diffuse or alveolar septal pattern, pleural disease, lymphadenopathy, and pulmonary cysts.⁴

Light chain deposition disease shares some clinical features with amyloidosis. However, the light chain fragments in this disease do not form amyloid fibrils and therefore do not stain positively with Congo red. The kidney is the most commonly involved organ.⁴

Neurofibromatosis type 1 is characterized by collections of neurofibromas, café-au-lait spots, and pigmented hamartomas in the iris (Lisch nodules).³⁵

In summary, patients in this group typically present with complications related to systemic involvement. Those with neurofibromatosis type 1 present with ophthalmologic, dermatologic, and neurologic manifestations. Amyloidosis and light chain deposition disease most commonly involve the renal system; their distinction will likely require tissue biopsy and Congo-red staining.

STEP 3: CHARACTERIZE THE RADIOGRAPHIC FEATURES

Characterization of pulmonary cysts and their distribution plays a key role in the diagnosis. Radiographically, cystic lung diseases can be subclassified into two major categories according to their cystic distribution:

• Discrete (focal or multifocal)
• Diffuse (unilobular or panlobular).^2,3

Discrete cystic lung diseases include congenital abnormalities, infectious diseases, and interstitial pneumonias.^2,3

Diffuse, panlobular cystic lung diseases include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, amyloidosis, light chain deposition disease, and neurofibromatosis type 1.^7,13,36–39

In addition, other associated radiographic findings play a major role in diagnosis.

Cysts in patients presenting with insidious dyspnea or spontaneous pneumothorax

Lymphangioleiomyomatosis. Cysts are seen in nearly all cases of advanced lymphangioleiomyomatosis, typically in a diffuse pattern, varying from 2 mm to 40 mm in diameter, and uniform in shape (Figure  2A).^7,8,40–42

Other radiographic features include vessels located at the periphery of the cysts (in contrast to the centrilobular pattern seen with emphysema), and chylous pleural effusions (in about 22% of patients).⁴⁰ Nodules are typically not seen with lymphangioleiomyomatosis, and if found represent type 2 pneumocyte hyperplasia.

Pulmonary Langerhans cell histiocytosis. Nodules measuring 1 to 10 mm in diameter and favoring a centrilobular location are often seen on computed tomography. Pulmonary cysts occur in about 61% of patients.^13,43 Cysts are variable in size and shape (Figure 2B), in contrast to their uniform appearance in lymphangioleiomyomatosis. Most cysts are less than 10 mm in diameter; however, they can be up to 80 mm.^13,43 Early in its course, nodules may predominate in the upper and middle lobes. Over time, diffuse cysts become more common and can be difficult to differentiate from advanced smoking-induced emphysema.⁴⁴

Birt-Hogg-Dubé syndrome. Approximately 70% to 100% of patients with Birt-Hogg-Dubé syndrome will have multiple pulmonary cysts detected on computed tomography. These cysts are characteristically basal and subpleural in location, with varying sizes and irregular shapes in otherwise normal lung parenchyma (Figure 2C).^36,45,46

Desquamative interstitial pneumonia. Pulmonary cysts are present on computed tomography in about 32% of patients.⁴⁷ They are usually round and less than 20 mm in diameter.⁴⁸ Ground-glass opacity is present in almost all cases of desquamative interstitial pneumonia, with a diffuse pattern in 25% to 44% of patients.^16,17,47

Pulmonary cysts occur in up to two-thirds of those with lymphocytic interstitial pneumonia. Cysts are usually multifocal and perivascular in distribution and have varying sizes and shapes (Figure 2D).²² Ground-glass opacity and poorly defined centrilobular nodules are also frequently seen. Other computed tomographic findings include thickening of the bronchovascular bundles, focal consolidation, interseptal lobular thickening, pleural thickening, and lymph node enlargement.²²

In summary, in this group of patients, diffuse panlobular cysts are due to lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, or Birt-Hogg-Dubé syndrome. Cysts due to lymphangioleiomyomatosis have a diffuse distribution, while those due to pulmonary Langerhans cell histiocytosis tend to be upper-lobe-predominant and in the early stages are associated with stellate centrilobular nodules. Cysts in Birt-Hogg-Dubé syndrome tend to be subpleural and those due to lymphocytic interstitial pneumonia are perivascular in distribution.

Cysts that are incidentally found or occur in patients with recurrent pneumonia

Congenital pulmonary airway malformation types 1, 2, and 4 (Figure 3A, 3B). Cysts are typically discrete and focal or multifocal in distribution, but cases of multilobar and bilateral distribution have also been reported.^27,49 The lower lobes are more often involved.⁴⁹ Cysts vary in size and shape and can contain air, fluid, or both.^27,49 Up to 50% of cases can occur in conjunction with pulmonary sequestration.⁵⁰

Pulmonary sequestration displays an anomalous arterial supply on computed tomography (Figure 3C). Other imaging findings include mass lesions (49%), cystic lesions (29%), cavitary lesions (12%), and bronchiectasis.³⁰ Air trapping can be seen in the adjacent lung. Lower lobe involvement accounts for more than 95% of total cases of sequestration.³⁰ The cysts are usually discrete or focal in distribution. Misdiagnosis of pulmonary sequestration is common, and can include pulmonary abscess, pneumonia, bronchiectasis, and lung cancer.³⁰

Bronchogenic cyst. Cyst contents generally demonstrate water attenuation, or higher attenuation if filled with proteinaceous/mucoid material or calcium deposits; air-fluid levels are seen in infected cysts.³² Intrapulmonary cysts have a predilection for the lower lobes and are usually discrete or focal in distribution.^31,32 Mediastinal cysts are usually homogeneous, solitary, and located in the middle mediastinum.³² Cysts vary in size from 20 to 90 mm, with  a mean diameter of 40 mm.³¹

In summary, in this group of cystic lung diseases, characteristic computed tomographic findings will suggest the diagnosis—air-filled cysts of varying sizes for congenital pulmonary airway malformation and anomalous vascular supply for pulmonary sequestration. Bronchogenic cysts will tend to have water or higher-than-water attenuation due to proteinaceous-mucoid material or calcium deposits.

Cysts in patients with signs and symptoms of primary pulmonary infections

P jirovecii pneumonia. Between 10% and 15% of patients have cysts, and about 18% present with spontaneous pneumothorax.⁵¹ Cysts in P jirovecii pneumonia vary in size from 15 to 85 mm in diameter and tend to occur in the upper lobes (Figure 4A).^51,52

Echinococcal infection. Echinococcal pulmonary cysts typically are single and located more often in the lower lobes (Figure 4B).^53,54 Cysts can be complicated by air-fluid levels, hydropneumothorax, or pneumothorax, or they can turn into cavitary lesions.

The diagnoses of these pulmonary infections are usually made by clinical and computed tomographic findings and depend less on detecting and characterizing lung cysts. Patients with P jirovecii pneumonia tend to have bilateral perihilar ground-glass opacities, while air-fluid levels suggest echinococcal infections. Cysts in this group of patients tend to be discrete or focal or multifocal in distribution, and vary in size.

Cysts in patients with primarily nonpulmonary signs and symptoms

Amyloidosis. Cyst formation is rare in amyloidosis.⁴ When present, cysts can be diffuse and scattered in distribution, in varying sizes (usually < 30 mm in diameter) and irregular shapes (Figure 5).^55,56

Pulmonary light chain deposition disease usually presents as linear opacities and small nodules on chest computed tomography. Numerous cysts that are diffuse in distribution and have no topographic predominance can also be present. They can progress in number and size and coalesce to form irregular shapes.⁵⁷

Neurofibromatosis type 1. In neurofibromatosis type 1, the most common radiographic presentations are bibasilar reticular opacities (50%), bullae (50%), and ground glass opacities (37%).⁵⁸ Well-formed cysts occur in up to 25% of patients and tend to be diffuse and smaller (2 to 18 mm in diameter), with upper lobe predominance.^58,59

In summary, in this group of patients, bibasilar reticular and ground-glass opacities suggest neurofibromatosis type 1, while nodules and linear opacities suggest amyloidosis or light chain deposition disease. Cysts tend to be diffuse with varying sizes.

STEP 4: PUT IT ALL TOGETHER

Diagnosis in insidious dyspnea or spontaneous pneumothorax

For patients who present with insidious dyspnea or spontaneous pneumothorax, the diagnosis of cystic lung disease can be made by characterizing the distribution, size, and shape of the cysts (Table 3).

Diffuse, panlobular distribution. Cystic lung diseases with this pattern include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, and Birt-Hogg-Dubé syndrome. In this group, cysts that are uniform in size and regular in shape are invariably due to lymphangioleiomyomatosis. Those with variable size and irregular shapes can be due to pulmonary Langerhans cell histiocytosis or Birt-Hogg-Dubé syndrome. Patients with pulmonary Langerhans cell histiocytosis tend to be smokers and their cysts tend to be upper- lobe-predominant. Those with Birt-Hogg-Dubé syndrome will likely have renal cancer or skin lesions; their cysts tend to be basilar and subpleural in distribution.

Cysts that are focal or multifocal and unilobular are due to lymphocytic interstitial pneumonia or desquamative interstitial pneumonia. Patients with lymphocytic interstitial pneumonia tend to have underlying connective tissue disease; those with desquamative interstitial pneumonia are almost always smokers. The definitive diagnosis for lymphocytic interstitial pneumonia or desquamative interstitial pneumonia can require a tissue biopsy.

Diagnosis in patients with incidentally found cysts or recurrent pneumonia

In those who present with incidentally found cysts or recurrent pneumonia, suspicion for a congenital lung malformation should be raised. Patients with a type 1, 2, or 4 congenital pulmonary airway malformation typically have air-filled cysts in varying sizes; those with pulmonary sequestration have an anomalous arterial supply in addition to cysts that are usually located in the lower lobes. Bronchogenic cysts tend to be larger, with attenuation equal to or greater than that of water, and distinguishing them from congenital pulmonary airway malformation will likely require surgical examination.

Diagnosis in patients with signs and symptoms of pulmonary infections

Patients with signs and symptoms of pulmonary infections should be investigated according to clinical risk factors for P jirovecii pneumonia or echinococcal infections.

Diagnosis in patients with primarily nonpulmonary presentations

The distinction between amyloidosis and neurofibromatosis type 1 can be made by the history and the clinical examination. However, a  definitive diagnosis of amyloidosis or light chain deposition disease requires tissue examination for the presence or absence of amyloid fibrils.

Air-filled pulmonary lesions commonly detected on chest computed tomography. Cystic lung lesions should be distinguished from other air-filled lesions to facilitate diagnosis. Primary care physicians play an integral role in the recognition of cystic lung disease.

The differential diagnosis of cystic lung disease is broad and includes isolated pulmonary, systemic, infectious, and congenital etiologies.

Here, we aim to provide a systematic, stepwise approach to help differentiate among the various cystic lung diseases and devise an algorithm for diagnosis. In doing so, we will discuss the clinical and radiographic features of many of these diseases:

• Lymphangioleiomyomatosis
• Birt-Hogg-Dubé syndrome
• Pulmonary Langerhans cell histiocytosis
• Interstitial pneumonia (desquamative interstitial pneumonia, lymphocytic interstitial pneumonia)
• Congenital cystic lung disease (congenital pulmonary airway malformation, pulmonary sequestration, bronchogenic cyst) Pulmonary infection
• Systemic disease (amyloidosis, light chain deposition disease, neurofibromatosis type 1).

STEP 1: RULE OUT CYST-MIMICS

A pulmonary cyst is a round, circumscribed space surrounded by an epithelial or fibrous wall of variable thickness.¹ On chest radiography and computed tomography, a cyst appears as a round parenchymal lucency or low-attenuating area with a well-defined interface with normal lung.¹ Cysts vary in wall thickness but  usually have a thin wall (< 2 mm) and occur without associated pulmonary emphysema.¹ They typically contain air but occasionally contain fluid or solid material.

A pulmonary cyst can be categorized as a bulla, bleb, or pneumatocele.

Pulmonary cysts can be categorized as bullae, blebs, or pneumatoceles

Bullae are larger than 1 cm in diameter, sharply demarcated by a thin wall, and usually accompanied by emphysematous changes in the adjacent lung.¹

Blebs are no larger than 1 cm in diameter, are located within the visceral pleura or the subpleural space, and appear on computed tomography as thin-walled air spaces that are contiguous with the pleura.¹ The distinction between a bleb and a bulla is of little clinical importance, and is often unnecessary.

Pneumatoceles are cysts that are frequently caused by acute pneumonia, trauma, or aspiration of hydrocarbon fluid, and are usually transient.¹

Mimics of pulmonary cysts include pulmonary cavities, emphysema, loculated pneumothoraces, honeycomb lung, and bronchiectasis (Figure 1).²

Pulmonary cavities differ from cysts in that their walls are typically thicker (usually > 4 mm).³

Emphysema differs from cystic lung disease as it typically leads to focal areas or regions of decreased lung attenuation that do not have defined walls.¹

Honeycombing refers to a cluster or row of cysts, 1 to 3 mm in wall thickness and typically 3 to 10 mm in diameter, that are associated with end-stage lung fibrosis.¹ They are typically subpleural in distribution and are accompanied by fibrotic features such as reticulation and traction bronchiectasis.¹

Bronchiectasis is dilation and distortion of bronchi and bronchioles and can be mistaken for cysts when viewed en face.¹

Loculated pneumothoraces can also mimic pulmonary cysts, but they typically fail to adhere to a defined anatomic unit and are subpleural in distribution.

STEP 2: CHARACTERIZE THE CLINICAL PRESENTATION

Clinical signs and symptoms of cystic lung disease play a key role in diagnosis (Table 1). For instance, spontaneous pneumothorax is commonly associated with diffuse cystic lung disease (lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome), while insidious dyspnea, with or without associated pneumothorax, is usually associated with the interstitial pneumonias (lymphocytic interstitial pneumonia and desquamative interstitial pneumonia).

In addition, congenital abnormalities of the lung can lead to cyst formation. These abnormalities, especially when associated with other congenital abnormalities, are often diagnosed in the prenatal and perinatal periods. However, some remain undetected until incidentally found later in adulthood or if superimposing infection develops.

Primary pulmonary infections can also cause parenchymal necrosis, which in turn cavitates or forms cysts.⁴

Lastly, cystic lung diseases can occur as part of a multiorgan or systemic illness in which the lung is one of the organs involved. Although usually diagnosed before the discovery of cysts or manifestations of pulmonary symptoms, they can present as a diagnostic challenge, especially when lung cysts are the initial presentation.bsence of amyloid fibrils.

In view of the features of the different types of cystic lung disease, adults with cystic lung disease can be grouped according to their typical clinical presentations (Table 2):

• Insidious dyspnea or spontaneous pneumothorax
• Incidentally found cysts or recurrent pneumonia
• Signs and symptoms of primary pulmonary infection
• Signs and symptoms that are primarily nonpulmonary.

Insidious dyspnea or spontaneous pneumothorax

Insidious dyspnea or spontaneous pneumothorax can be manifestations of lymphangioleiomyomatosis, Birt-Hogg-Dubé syndrome, pulmonary Langerhans cell histiocytosis, desquamative interstitial pneumonia, or lymphocytic interstitial pneumonia.

Lymphangioleiomyomatosis is characterized by abnormal cellular proliferation within the lung, kidney, lymphatic system, or any combination.⁵ The peak prevalence is in the third to fourth decades of life, and most patients are women of childbearing age.⁶ In addition to progressive dyspnea on exertion and pneumothorax, other signs and symptoms include hemoptysis, nonproductive cough, chylous pleural effusion, and ascites.^7,8

Birt-Hogg-Dubé syndrome is caused by germline mutations in the folliculin (FLCN) gene.⁹ It is characterized by skin fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and renal cancer.¹⁰

Pulmonary Langerhans cell histiocytosis is part of the spectrum of Langerhans cell histiocytosis that, in addition to the lungs, can also involve the bone, pituitary gland, thyroid, skin, lymph nodes, and liver.¹¹ It occurs almost exclusively in smokers, affecting individuals in their 20s and 30s, with no gender predilection.^12,13 In addition to nonproductive cough and dyspnea, patients can also present with fever, anorexia, and weight loss,¹³ but approximately 25% of patients are asymptomatic.¹⁴

Desquamative interstitial pneumonia is an idiopathic interstitial pneumonia that, like pulmonary Langerhans cell histiocytosis, is seen almost exclusively in current or former smokers, who account for about 90% of patients with this disease. It affects almost twice as many men as women.^15,16 The mean age at onset is 42 to 46.^15,16 In addition to insidious cough and dyspnea, digital clubbing develops in 26% to 40% of patients.^16,17

Lymphocytic interstitial pneumonia is another rare idiopathic pneumonia, usually associated with connective tissue disease, Sjögren syndrome, immunodeficiencies, and viral infections.^18­–21 It is more common in women, presenting between the 4th and 7th decades of life, with a mean age at diagnosis of 50 to 56.^18,22 In addition to progressive dyspnea and cough, other symptoms include weight loss, pleuritic pain, arthralgias, fatigue, night sweats, and fever.²³

In summary, in this clinical group, lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome should be considered when patients present with spontaneous pneumothorax; those with Birt-Hogg-Dubé syndrome also present with skin lesions or renal cancer. In patients with progressive dyspnea and cough, lymphocytic interstitial pneumonia should be considered in those with a known history of connective tissue disease or immunodeficiency. Pulmonary Langerhans cell histiocytosis typically presents at a younger age (20 to 30 years old) than desquamative interstitial pneumonia (smokers in their 40s). Making the distinction, however, will likely require imaging with computed tomography.

Incidentally found cysts or recurrent pneumonia

Incidentally found cysts or recurrent pneumonia can be manifestations of congenital pulmonary airway malformation, pulmonary sequestration, or bronchogenic cyst.

Congenital pulmonary airway malformation, of which there are five types, is the most common pulmonary congenital abnormality. It accounts for up to 95% of cases of congenital cystic lung disease.^24,25 About 85% of cases are detected in the prenatal or perinatal periods.²⁶ Late-onset congenital pulmonary airway malformation (arising in childhood to adulthood) presents with recurrent pneumonia in about 75% of cases and can be misdiagnosed as lung abscess, pulmonary tuberculosis, or bronchiectasis.²⁷

Pulmonary sequestration, the second most common pulmonary congenital abnormality, is characterized by a portion of lung that does not connect to the tracheobronchial tree and has its own systemic arterial supply.²⁴ Intralobar sequestration, which shares the pleural investment with normal lung, accounts for about 80% of cases of pulmonary sequestration.^28–30 In addition to signs or symptoms of pulmonary infection, patients with pulmonary sequestration can remain asymp-
tomatic (about 25% of cases), or can present with hemoptysis or hemothorax.^28–30 In adults, the typical age at presentation is between 20 and 25.^29,30

Bronchogenic cyst is usually life-threatening in children. In adults, it commonly causes cough and chest pain.³¹ Hemoptysis, dysphagia, hoarseness, and diaphragmatic paralysis can also occur.^32,33 The mean age at diagnosis in adults is 35 to 40.^31,32

In summary, most cases of recurrent pneumonia with cysts are due to congenital pulmonary airway malformation. Pulmonary sequestration is the second most common cause of cystic lung disease in this group. Bronchogenic cyst is usually fatal in fetal development; smaller cysts can go unnoticed during the earlier years and are later found incidentally as imaging abnormalities in adults.

Signs and symptoms of primary pulmonary infections

Signs and symptoms of primary pulmonary infections can be due to Pneumocystis jirovecii pneumonia or echinococcal infections.

P jirovecii pneumonia commonly develops in patients with human immunodeficiency virus infection and low CD4 counts, recipients of hematologic or solid-organ transplants, and those receiving immunosuppressive therapy (eg, glucocorticoids or chemotherapy).

Echinococcal infections (with Echinococcus granulosus or multilocularis species) are more common in less-developed countries such as those in South America or the Middle East, in China, or in patients who have traveled to endemic areas.³⁴

In summary, cystic lung disease in patients with primary pulmonary infections can be diagnosed by the patient’s clinical history and risk factors for infections. Those with human immunodeficiency virus infection and other causes of immunodeficiency are predisposed to P jirovecii pneumonia. Echinococcal infections occur in those with a history of travel to an endemic area.

Primarily nonpulmonary signs and symptoms

If the patient has primarily nonpulmonary signs and symptoms, think about pulmonary amyloidosis, light chain deposition disease, and neurofibromatosis type 1.

Pulmonary amyloidosis has a variety of manifestations, including tracheobronchial disease, nodular parenchymal disease, diffuse or alveolar septal pattern, pleural disease, lymphadenopathy, and pulmonary cysts.⁴

Light chain deposition disease shares some clinical features with amyloidosis. However, the light chain fragments in this disease do not form amyloid fibrils and therefore do not stain positively with Congo red. The kidney is the most commonly involved organ.⁴

Neurofibromatosis type 1 is characterized by collections of neurofibromas, café-au-lait spots, and pigmented hamartomas in the iris (Lisch nodules).³⁵

In summary, patients in this group typically present with complications related to systemic involvement. Those with neurofibromatosis type 1 present with ophthalmologic, dermatologic, and neurologic manifestations. Amyloidosis and light chain deposition disease most commonly involve the renal system; their distinction will likely require tissue biopsy and Congo-red staining.

STEP 3: CHARACTERIZE THE RADIOGRAPHIC FEATURES

Characterization of pulmonary cysts and their distribution plays a key role in the diagnosis. Radiographically, cystic lung diseases can be subclassified into two major categories according to their cystic distribution:

• Discrete (focal or multifocal)
• Diffuse (unilobular or panlobular).^2,3

Discrete cystic lung diseases include congenital abnormalities, infectious diseases, and interstitial pneumonias.^2,3

Diffuse, panlobular cystic lung diseases include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, amyloidosis, light chain deposition disease, and neurofibromatosis type 1.^7,13,36–39

In addition, other associated radiographic findings play a major role in diagnosis.

Cysts in patients presenting with insidious dyspnea or spontaneous pneumothorax

Lymphangioleiomyomatosis. Cysts are seen in nearly all cases of advanced lymphangioleiomyomatosis, typically in a diffuse pattern, varying from 2 mm to 40 mm in diameter, and uniform in shape (Figure  2A).^7,8,40–42

Other radiographic features include vessels located at the periphery of the cysts (in contrast to the centrilobular pattern seen with emphysema), and chylous pleural effusions (in about 22% of patients).⁴⁰ Nodules are typically not seen with lymphangioleiomyomatosis, and if found represent type 2 pneumocyte hyperplasia.

Pulmonary Langerhans cell histiocytosis. Nodules measuring 1 to 10 mm in diameter and favoring a centrilobular location are often seen on computed tomography. Pulmonary cysts occur in about 61% of patients.^13,43 Cysts are variable in size and shape (Figure 2B), in contrast to their uniform appearance in lymphangioleiomyomatosis. Most cysts are less than 10 mm in diameter; however, they can be up to 80 mm.^13,43 Early in its course, nodules may predominate in the upper and middle lobes. Over time, diffuse cysts become more common and can be difficult to differentiate from advanced smoking-induced emphysema.⁴⁴

Birt-Hogg-Dubé syndrome. Approximately 70% to 100% of patients with Birt-Hogg-Dubé syndrome will have multiple pulmonary cysts detected on computed tomography. These cysts are characteristically basal and subpleural in location, with varying sizes and irregular shapes in otherwise normal lung parenchyma (Figure 2C).^36,45,46

Desquamative interstitial pneumonia. Pulmonary cysts are present on computed tomography in about 32% of patients.⁴⁷ They are usually round and less than 20 mm in diameter.⁴⁸ Ground-glass opacity is present in almost all cases of desquamative interstitial pneumonia, with a diffuse pattern in 25% to 44% of patients.^16,17,47

Pulmonary cysts occur in up to two-thirds of those with lymphocytic interstitial pneumonia. Cysts are usually multifocal and perivascular in distribution and have varying sizes and shapes (Figure 2D).²² Ground-glass opacity and poorly defined centrilobular nodules are also frequently seen. Other computed tomographic findings include thickening of the bronchovascular bundles, focal consolidation, interseptal lobular thickening, pleural thickening, and lymph node enlargement.²²

In summary, in this group of patients, diffuse panlobular cysts are due to lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, or Birt-Hogg-Dubé syndrome. Cysts due to lymphangioleiomyomatosis have a diffuse distribution, while those due to pulmonary Langerhans cell histiocytosis tend to be upper-lobe-predominant and in the early stages are associated with stellate centrilobular nodules. Cysts in Birt-Hogg-Dubé syndrome tend to be subpleural and those due to lymphocytic interstitial pneumonia are perivascular in distribution.

Cysts that are incidentally found or occur in patients with recurrent pneumonia

Congenital pulmonary airway malformation types 1, 2, and 4 (Figure 3A, 3B). Cysts are typically discrete and focal or multifocal in distribution, but cases of multilobar and bilateral distribution have also been reported.^27,49 The lower lobes are more often involved.⁴⁹ Cysts vary in size and shape and can contain air, fluid, or both.^27,49 Up to 50% of cases can occur in conjunction with pulmonary sequestration.⁵⁰

Pulmonary sequestration displays an anomalous arterial supply on computed tomography (Figure 3C). Other imaging findings include mass lesions (49%), cystic lesions (29%), cavitary lesions (12%), and bronchiectasis.³⁰ Air trapping can be seen in the adjacent lung. Lower lobe involvement accounts for more than 95% of total cases of sequestration.³⁰ The cysts are usually discrete or focal in distribution. Misdiagnosis of pulmonary sequestration is common, and can include pulmonary abscess, pneumonia, bronchiectasis, and lung cancer.³⁰

Bronchogenic cyst. Cyst contents generally demonstrate water attenuation, or higher attenuation if filled with proteinaceous/mucoid material or calcium deposits; air-fluid levels are seen in infected cysts.³² Intrapulmonary cysts have a predilection for the lower lobes and are usually discrete or focal in distribution.^31,32 Mediastinal cysts are usually homogeneous, solitary, and located in the middle mediastinum.³² Cysts vary in size from 20 to 90 mm, with  a mean diameter of 40 mm.³¹

In summary, in this group of cystic lung diseases, characteristic computed tomographic findings will suggest the diagnosis—air-filled cysts of varying sizes for congenital pulmonary airway malformation and anomalous vascular supply for pulmonary sequestration. Bronchogenic cysts will tend to have water or higher-than-water attenuation due to proteinaceous-mucoid material or calcium deposits.

Cysts in patients with signs and symptoms of primary pulmonary infections

P jirovecii pneumonia. Between 10% and 15% of patients have cysts, and about 18% present with spontaneous pneumothorax.⁵¹ Cysts in P jirovecii pneumonia vary in size from 15 to 85 mm in diameter and tend to occur in the upper lobes (Figure 4A).^51,52

Echinococcal infection. Echinococcal pulmonary cysts typically are single and located more often in the lower lobes (Figure 4B).^53,54 Cysts can be complicated by air-fluid levels, hydropneumothorax, or pneumothorax, or they can turn into cavitary lesions.

The diagnoses of these pulmonary infections are usually made by clinical and computed tomographic findings and depend less on detecting and characterizing lung cysts. Patients with P jirovecii pneumonia tend to have bilateral perihilar ground-glass opacities, while air-fluid levels suggest echinococcal infections. Cysts in this group of patients tend to be discrete or focal or multifocal in distribution, and vary in size.

Cysts in patients with primarily nonpulmonary signs and symptoms

Amyloidosis. Cyst formation is rare in amyloidosis.⁴ When present, cysts can be diffuse and scattered in distribution, in varying sizes (usually < 30 mm in diameter) and irregular shapes (Figure 5).^55,56

Pulmonary light chain deposition disease usually presents as linear opacities and small nodules on chest computed tomography. Numerous cysts that are diffuse in distribution and have no topographic predominance can also be present. They can progress in number and size and coalesce to form irregular shapes.⁵⁷

Neurofibromatosis type 1. In neurofibromatosis type 1, the most common radiographic presentations are bibasilar reticular opacities (50%), bullae (50%), and ground glass opacities (37%).⁵⁸ Well-formed cysts occur in up to 25% of patients and tend to be diffuse and smaller (2 to 18 mm in diameter), with upper lobe predominance.^58,59

In summary, in this group of patients, bibasilar reticular and ground-glass opacities suggest neurofibromatosis type 1, while nodules and linear opacities suggest amyloidosis or light chain deposition disease. Cysts tend to be diffuse with varying sizes.

STEP 4: PUT IT ALL TOGETHER

Diagnosis in insidious dyspnea or spontaneous pneumothorax

For patients who present with insidious dyspnea or spontaneous pneumothorax, the diagnosis of cystic lung disease can be made by characterizing the distribution, size, and shape of the cysts (Table 3).

Diffuse, panlobular distribution. Cystic lung diseases with this pattern include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, and Birt-Hogg-Dubé syndrome. In this group, cysts that are uniform in size and regular in shape are invariably due to lymphangioleiomyomatosis. Those with variable size and irregular shapes can be due to pulmonary Langerhans cell histiocytosis or Birt-Hogg-Dubé syndrome. Patients with pulmonary Langerhans cell histiocytosis tend to be smokers and their cysts tend to be upper- lobe-predominant. Those with Birt-Hogg-Dubé syndrome will likely have renal cancer or skin lesions; their cysts tend to be basilar and subpleural in distribution.

Cysts that are focal or multifocal and unilobular are due to lymphocytic interstitial pneumonia or desquamative interstitial pneumonia. Patients with lymphocytic interstitial pneumonia tend to have underlying connective tissue disease; those with desquamative interstitial pneumonia are almost always smokers. The definitive diagnosis for lymphocytic interstitial pneumonia or desquamative interstitial pneumonia can require a tissue biopsy.

Diagnosis in patients with incidentally found cysts or recurrent pneumonia

In those who present with incidentally found cysts or recurrent pneumonia, suspicion for a congenital lung malformation should be raised. Patients with a type 1, 2, or 4 congenital pulmonary airway malformation typically have air-filled cysts in varying sizes; those with pulmonary sequestration have an anomalous arterial supply in addition to cysts that are usually located in the lower lobes. Bronchogenic cysts tend to be larger, with attenuation equal to or greater than that of water, and distinguishing them from congenital pulmonary airway malformation will likely require surgical examination.

Diagnosis in patients with signs and symptoms of pulmonary infections

Patients with signs and symptoms of pulmonary infections should be investigated according to clinical risk factors for P jirovecii pneumonia or echinococcal infections.

Diagnosis in patients with primarily nonpulmonary presentations

The distinction between amyloidosis and neurofibromatosis type 1 can be made by the history and the clinical examination. However, a  definitive diagnosis of amyloidosis or light chain deposition disease requires tissue examination for the presence or absence of amyloid fibrils.

Air-filled pulmonary lesions commonly detected on chest computed tomography. Cystic lung lesions should be distinguished from other air-filled lesions to facilitate diagnosis. Primary care physicians play an integral role in the recognition of cystic lung disease.

The differential diagnosis of cystic lung disease is broad and includes isolated pulmonary, systemic, infectious, and congenital etiologies.

Here, we aim to provide a systematic, stepwise approach to help differentiate among the various cystic lung diseases and devise an algorithm for diagnosis. In doing so, we will discuss the clinical and radiographic features of many of these diseases:

• Lymphangioleiomyomatosis
• Birt-Hogg-Dubé syndrome
• Pulmonary Langerhans cell histiocytosis
• Interstitial pneumonia (desquamative interstitial pneumonia, lymphocytic interstitial pneumonia)
• Congenital cystic lung disease (congenital pulmonary airway malformation, pulmonary sequestration, bronchogenic cyst) Pulmonary infection
• Systemic disease (amyloidosis, light chain deposition disease, neurofibromatosis type 1).

STEP 1: RULE OUT CYST-MIMICS

A pulmonary cyst is a round, circumscribed space surrounded by an epithelial or fibrous wall of variable thickness.¹ On chest radiography and computed tomography, a cyst appears as a round parenchymal lucency or low-attenuating area with a well-defined interface with normal lung.¹ Cysts vary in wall thickness but  usually have a thin wall (< 2 mm) and occur without associated pulmonary emphysema.¹ They typically contain air but occasionally contain fluid or solid material.

A pulmonary cyst can be categorized as a bulla, bleb, or pneumatocele.

Pulmonary cysts can be categorized as bullae, blebs, or pneumatoceles

Bullae are larger than 1 cm in diameter, sharply demarcated by a thin wall, and usually accompanied by emphysematous changes in the adjacent lung.¹

Blebs are no larger than 1 cm in diameter, are located within the visceral pleura or the subpleural space, and appear on computed tomography as thin-walled air spaces that are contiguous with the pleura.¹ The distinction between a bleb and a bulla is of little clinical importance, and is often unnecessary.

Pneumatoceles are cysts that are frequently caused by acute pneumonia, trauma, or aspiration of hydrocarbon fluid, and are usually transient.¹

Mimics of pulmonary cysts include pulmonary cavities, emphysema, loculated pneumothoraces, honeycomb lung, and bronchiectasis (Figure 1).²

Pulmonary cavities differ from cysts in that their walls are typically thicker (usually > 4 mm).³

Emphysema differs from cystic lung disease as it typically leads to focal areas or regions of decreased lung attenuation that do not have defined walls.¹

Honeycombing refers to a cluster or row of cysts, 1 to 3 mm in wall thickness and typically 3 to 10 mm in diameter, that are associated with end-stage lung fibrosis.¹ They are typically subpleural in distribution and are accompanied by fibrotic features such as reticulation and traction bronchiectasis.¹

Bronchiectasis is dilation and distortion of bronchi and bronchioles and can be mistaken for cysts when viewed en face.¹

Loculated pneumothoraces can also mimic pulmonary cysts, but they typically fail to adhere to a defined anatomic unit and are subpleural in distribution.

STEP 2: CHARACTERIZE THE CLINICAL PRESENTATION

Clinical signs and symptoms of cystic lung disease play a key role in diagnosis (Table 1). For instance, spontaneous pneumothorax is commonly associated with diffuse cystic lung disease (lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome), while insidious dyspnea, with or without associated pneumothorax, is usually associated with the interstitial pneumonias (lymphocytic interstitial pneumonia and desquamative interstitial pneumonia).

In addition, congenital abnormalities of the lung can lead to cyst formation. These abnormalities, especially when associated with other congenital abnormalities, are often diagnosed in the prenatal and perinatal periods. However, some remain undetected until incidentally found later in adulthood or if superimposing infection develops.

Primary pulmonary infections can also cause parenchymal necrosis, which in turn cavitates or forms cysts.⁴

Lastly, cystic lung diseases can occur as part of a multiorgan or systemic illness in which the lung is one of the organs involved. Although usually diagnosed before the discovery of cysts or manifestations of pulmonary symptoms, they can present as a diagnostic challenge, especially when lung cysts are the initial presentation.bsence of amyloid fibrils.

In view of the features of the different types of cystic lung disease, adults with cystic lung disease can be grouped according to their typical clinical presentations (Table 2):

• Insidious dyspnea or spontaneous pneumothorax
• Incidentally found cysts or recurrent pneumonia
• Signs and symptoms of primary pulmonary infection
• Signs and symptoms that are primarily nonpulmonary.

Insidious dyspnea or spontaneous pneumothorax

Insidious dyspnea or spontaneous pneumothorax can be manifestations of lymphangioleiomyomatosis, Birt-Hogg-Dubé syndrome, pulmonary Langerhans cell histiocytosis, desquamative interstitial pneumonia, or lymphocytic interstitial pneumonia.

Lymphangioleiomyomatosis is characterized by abnormal cellular proliferation within the lung, kidney, lymphatic system, or any combination.⁵ The peak prevalence is in the third to fourth decades of life, and most patients are women of childbearing age.⁶ In addition to progressive dyspnea on exertion and pneumothorax, other signs and symptoms include hemoptysis, nonproductive cough, chylous pleural effusion, and ascites.^7,8

Birt-Hogg-Dubé syndrome is caused by germline mutations in the folliculin (FLCN) gene.⁹ It is characterized by skin fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and renal cancer.¹⁰

Pulmonary Langerhans cell histiocytosis is part of the spectrum of Langerhans cell histiocytosis that, in addition to the lungs, can also involve the bone, pituitary gland, thyroid, skin, lymph nodes, and liver.¹¹ It occurs almost exclusively in smokers, affecting individuals in their 20s and 30s, with no gender predilection.^12,13 In addition to nonproductive cough and dyspnea, patients can also present with fever, anorexia, and weight loss,¹³ but approximately 25% of patients are asymptomatic.¹⁴

Desquamative interstitial pneumonia is an idiopathic interstitial pneumonia that, like pulmonary Langerhans cell histiocytosis, is seen almost exclusively in current or former smokers, who account for about 90% of patients with this disease. It affects almost twice as many men as women.^15,16 The mean age at onset is 42 to 46.^15,16 In addition to insidious cough and dyspnea, digital clubbing develops in 26% to 40% of patients.^16,17

Lymphocytic interstitial pneumonia is another rare idiopathic pneumonia, usually associated with connective tissue disease, Sjögren syndrome, immunodeficiencies, and viral infections.^18­–21 It is more common in women, presenting between the 4th and 7th decades of life, with a mean age at diagnosis of 50 to 56.^18,22 In addition to progressive dyspnea and cough, other symptoms include weight loss, pleuritic pain, arthralgias, fatigue, night sweats, and fever.²³

In summary, in this clinical group, lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome should be considered when patients present with spontaneous pneumothorax; those with Birt-Hogg-Dubé syndrome also present with skin lesions or renal cancer. In patients with progressive dyspnea and cough, lymphocytic interstitial pneumonia should be considered in those with a known history of connective tissue disease or immunodeficiency. Pulmonary Langerhans cell histiocytosis typically presents at a younger age (20 to 30 years old) than desquamative interstitial pneumonia (smokers in their 40s). Making the distinction, however, will likely require imaging with computed tomography.

Incidentally found cysts or recurrent pneumonia

Incidentally found cysts or recurrent pneumonia can be manifestations of congenital pulmonary airway malformation, pulmonary sequestration, or bronchogenic cyst.

Congenital pulmonary airway malformation, of which there are five types, is the most common pulmonary congenital abnormality. It accounts for up to 95% of cases of congenital cystic lung disease.^24,25 About 85% of cases are detected in the prenatal or perinatal periods.²⁶ Late-onset congenital pulmonary airway malformation (arising in childhood to adulthood) presents with recurrent pneumonia in about 75% of cases and can be misdiagnosed as lung abscess, pulmonary tuberculosis, or bronchiectasis.²⁷

Pulmonary sequestration, the second most common pulmonary congenital abnormality, is characterized by a portion of lung that does not connect to the tracheobronchial tree and has its own systemic arterial supply.²⁴ Intralobar sequestration, which shares the pleural investment with normal lung, accounts for about 80% of cases of pulmonary sequestration.^28–30 In addition to signs or symptoms of pulmonary infection, patients with pulmonary sequestration can remain asymp-
tomatic (about 25% of cases), or can present with hemoptysis or hemothorax.^28–30 In adults, the typical age at presentation is between 20 and 25.^29,30

Bronchogenic cyst is usually life-threatening in children. In adults, it commonly causes cough and chest pain.³¹ Hemoptysis, dysphagia, hoarseness, and diaphragmatic paralysis can also occur.^32,33 The mean age at diagnosis in adults is 35 to 40.^31,32

In summary, most cases of recurrent pneumonia with cysts are due to congenital pulmonary airway malformation. Pulmonary sequestration is the second most common cause of cystic lung disease in this group. Bronchogenic cyst is usually fatal in fetal development; smaller cysts can go unnoticed during the earlier years and are later found incidentally as imaging abnormalities in adults.

Signs and symptoms of primary pulmonary infections

Signs and symptoms of primary pulmonary infections can be due to Pneumocystis jirovecii pneumonia or echinococcal infections.

P jirovecii pneumonia commonly develops in patients with human immunodeficiency virus infection and low CD4 counts, recipients of hematologic or solid-organ transplants, and those receiving immunosuppressive therapy (eg, glucocorticoids or chemotherapy).

Echinococcal infections (with Echinococcus granulosus or multilocularis species) are more common in less-developed countries such as those in South America or the Middle East, in China, or in patients who have traveled to endemic areas.³⁴

In summary, cystic lung disease in patients with primary pulmonary infections can be diagnosed by the patient’s clinical history and risk factors for infections. Those with human immunodeficiency virus infection and other causes of immunodeficiency are predisposed to P jirovecii pneumonia. Echinococcal infections occur in those with a history of travel to an endemic area.

Primarily nonpulmonary signs and symptoms

If the patient has primarily nonpulmonary signs and symptoms, think about pulmonary amyloidosis, light chain deposition disease, and neurofibromatosis type 1.

Pulmonary amyloidosis has a variety of manifestations, including tracheobronchial disease, nodular parenchymal disease, diffuse or alveolar septal pattern, pleural disease, lymphadenopathy, and pulmonary cysts.⁴

Light chain deposition disease shares some clinical features with amyloidosis. However, the light chain fragments in this disease do not form amyloid fibrils and therefore do not stain positively with Congo red. The kidney is the most commonly involved organ.⁴

Neurofibromatosis type 1 is characterized by collections of neurofibromas, café-au-lait spots, and pigmented hamartomas in the iris (Lisch nodules).³⁵

In summary, patients in this group typically present with complications related to systemic involvement. Those with neurofibromatosis type 1 present with ophthalmologic, dermatologic, and neurologic manifestations. Amyloidosis and light chain deposition disease most commonly involve the renal system; their distinction will likely require tissue biopsy and Congo-red staining.

STEP 3: CHARACTERIZE THE RADIOGRAPHIC FEATURES

Characterization of pulmonary cysts and their distribution plays a key role in the diagnosis. Radiographically, cystic lung diseases can be subclassified into two major categories according to their cystic distribution:

• Discrete (focal or multifocal)
• Diffuse (unilobular or panlobular).^2,3

Discrete cystic lung diseases include congenital abnormalities, infectious diseases, and interstitial pneumonias.^2,3

Diffuse, panlobular cystic lung diseases include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, amyloidosis, light chain deposition disease, and neurofibromatosis type 1.^7,13,36–39

In addition, other associated radiographic findings play a major role in diagnosis.

Cysts in patients presenting with insidious dyspnea or spontaneous pneumothorax

Lymphangioleiomyomatosis. Cysts are seen in nearly all cases of advanced lymphangioleiomyomatosis, typically in a diffuse pattern, varying from 2 mm to 40 mm in diameter, and uniform in shape (Figure  2A).^7,8,40–42

Other radiographic features include vessels located at the periphery of the cysts (in contrast to the centrilobular pattern seen with emphysema), and chylous pleural effusions (in about 22% of patients).⁴⁰ Nodules are typically not seen with lymphangioleiomyomatosis, and if found represent type 2 pneumocyte hyperplasia.

Pulmonary Langerhans cell histiocytosis. Nodules measuring 1 to 10 mm in diameter and favoring a centrilobular location are often seen on computed tomography. Pulmonary cysts occur in about 61% of patients.^13,43 Cysts are variable in size and shape (Figure 2B), in contrast to their uniform appearance in lymphangioleiomyomatosis. Most cysts are less than 10 mm in diameter; however, they can be up to 80 mm.^13,43 Early in its course, nodules may predominate in the upper and middle lobes. Over time, diffuse cysts become more common and can be difficult to differentiate from advanced smoking-induced emphysema.⁴⁴

Birt-Hogg-Dubé syndrome. Approximately 70% to 100% of patients with Birt-Hogg-Dubé syndrome will have multiple pulmonary cysts detected on computed tomography. These cysts are characteristically basal and subpleural in location, with varying sizes and irregular shapes in otherwise normal lung parenchyma (Figure 2C).^36,45,46

Desquamative interstitial pneumonia. Pulmonary cysts are present on computed tomography in about 32% of patients.⁴⁷ They are usually round and less than 20 mm in diameter.⁴⁸ Ground-glass opacity is present in almost all cases of desquamative interstitial pneumonia, with a diffuse pattern in 25% to 44% of patients.^16,17,47

Pulmonary cysts occur in up to two-thirds of those with lymphocytic interstitial pneumonia. Cysts are usually multifocal and perivascular in distribution and have varying sizes and shapes (Figure 2D).²² Ground-glass opacity and poorly defined centrilobular nodules are also frequently seen. Other computed tomographic findings include thickening of the bronchovascular bundles, focal consolidation, interseptal lobular thickening, pleural thickening, and lymph node enlargement.²²

In summary, in this group of patients, diffuse panlobular cysts are due to lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, or Birt-Hogg-Dubé syndrome. Cysts due to lymphangioleiomyomatosis have a diffuse distribution, while those due to pulmonary Langerhans cell histiocytosis tend to be upper-lobe-predominant and in the early stages are associated with stellate centrilobular nodules. Cysts in Birt-Hogg-Dubé syndrome tend to be subpleural and those due to lymphocytic interstitial pneumonia are perivascular in distribution.

Cysts that are incidentally found or occur in patients with recurrent pneumonia

Congenital pulmonary airway malformation types 1, 2, and 4 (Figure 3A, 3B). Cysts are typically discrete and focal or multifocal in distribution, but cases of multilobar and bilateral distribution have also been reported.^27,49 The lower lobes are more often involved.⁴⁹ Cysts vary in size and shape and can contain air, fluid, or both.^27,49 Up to 50% of cases can occur in conjunction with pulmonary sequestration.⁵⁰

Pulmonary sequestration displays an anomalous arterial supply on computed tomography (Figure 3C). Other imaging findings include mass lesions (49%), cystic lesions (29%), cavitary lesions (12%), and bronchiectasis.³⁰ Air trapping can be seen in the adjacent lung. Lower lobe involvement accounts for more than 95% of total cases of sequestration.³⁰ The cysts are usually discrete or focal in distribution. Misdiagnosis of pulmonary sequestration is common, and can include pulmonary abscess, pneumonia, bronchiectasis, and lung cancer.³⁰

Bronchogenic cyst. Cyst contents generally demonstrate water attenuation, or higher attenuation if filled with proteinaceous/mucoid material or calcium deposits; air-fluid levels are seen in infected cysts.³² Intrapulmonary cysts have a predilection for the lower lobes and are usually discrete or focal in distribution.^31,32 Mediastinal cysts are usually homogeneous, solitary, and located in the middle mediastinum.³² Cysts vary in size from 20 to 90 mm, with  a mean diameter of 40 mm.³¹

In summary, in this group of cystic lung diseases, characteristic computed tomographic findings will suggest the diagnosis—air-filled cysts of varying sizes for congenital pulmonary airway malformation and anomalous vascular supply for pulmonary sequestration. Bronchogenic cysts will tend to have water or higher-than-water attenuation due to proteinaceous-mucoid material or calcium deposits.

Cysts in patients with signs and symptoms of primary pulmonary infections

P jirovecii pneumonia. Between 10% and 15% of patients have cysts, and about 18% present with spontaneous pneumothorax.⁵¹ Cysts in P jirovecii pneumonia vary in size from 15 to 85 mm in diameter and tend to occur in the upper lobes (Figure 4A).^51,52

Echinococcal infection. Echinococcal pulmonary cysts typically are single and located more often in the lower lobes (Figure 4B).^53,54 Cysts can be complicated by air-fluid levels, hydropneumothorax, or pneumothorax, or they can turn into cavitary lesions.

The diagnoses of these pulmonary infections are usually made by clinical and computed tomographic findings and depend less on detecting and characterizing lung cysts. Patients with P jirovecii pneumonia tend to have bilateral perihilar ground-glass opacities, while air-fluid levels suggest echinococcal infections. Cysts in this group of patients tend to be discrete or focal or multifocal in distribution, and vary in size.

Cysts in patients with primarily nonpulmonary signs and symptoms

Amyloidosis. Cyst formation is rare in amyloidosis.⁴ When present, cysts can be diffuse and scattered in distribution, in varying sizes (usually < 30 mm in diameter) and irregular shapes (Figure 5).^55,56

Pulmonary light chain deposition disease usually presents as linear opacities and small nodules on chest computed tomography. Numerous cysts that are diffuse in distribution and have no topographic predominance can also be present. They can progress in number and size and coalesce to form irregular shapes.⁵⁷

Neurofibromatosis type 1. In neurofibromatosis type 1, the most common radiographic presentations are bibasilar reticular opacities (50%), bullae (50%), and ground glass opacities (37%).⁵⁸ Well-formed cysts occur in up to 25% of patients and tend to be diffuse and smaller (2 to 18 mm in diameter), with upper lobe predominance.^58,59

In summary, in this group of patients, bibasilar reticular and ground-glass opacities suggest neurofibromatosis type 1, while nodules and linear opacities suggest amyloidosis or light chain deposition disease. Cysts tend to be diffuse with varying sizes.

STEP 4: PUT IT ALL TOGETHER

Diagnosis in insidious dyspnea or spontaneous pneumothorax

For patients who present with insidious dyspnea or spontaneous pneumothorax, the diagnosis of cystic lung disease can be made by characterizing the distribution, size, and shape of the cysts (Table 3).

Diffuse, panlobular distribution. Cystic lung diseases with this pattern include lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, and Birt-Hogg-Dubé syndrome. In this group, cysts that are uniform in size and regular in shape are invariably due to lymphangioleiomyomatosis. Those with variable size and irregular shapes can be due to pulmonary Langerhans cell histiocytosis or Birt-Hogg-Dubé syndrome. Patients with pulmonary Langerhans cell histiocytosis tend to be smokers and their cysts tend to be upper- lobe-predominant. Those with Birt-Hogg-Dubé syndrome will likely have renal cancer or skin lesions; their cysts tend to be basilar and subpleural in distribution.

Cysts that are focal or multifocal and unilobular are due to lymphocytic interstitial pneumonia or desquamative interstitial pneumonia. Patients with lymphocytic interstitial pneumonia tend to have underlying connective tissue disease; those with desquamative interstitial pneumonia are almost always smokers. The definitive diagnosis for lymphocytic interstitial pneumonia or desquamative interstitial pneumonia can require a tissue biopsy.

Diagnosis in patients with incidentally found cysts or recurrent pneumonia

In those who present with incidentally found cysts or recurrent pneumonia, suspicion for a congenital lung malformation should be raised. Patients with a type 1, 2, or 4 congenital pulmonary airway malformation typically have air-filled cysts in varying sizes; those with pulmonary sequestration have an anomalous arterial supply in addition to cysts that are usually located in the lower lobes. Bronchogenic cysts tend to be larger, with attenuation equal to or greater than that of water, and distinguishing them from congenital pulmonary airway malformation will likely require surgical examination.

Diagnosis in patients with signs and symptoms of pulmonary infections

Patients with signs and symptoms of pulmonary infections should be investigated according to clinical risk factors for P jirovecii pneumonia or echinococcal infections.

Diagnosis in patients with primarily nonpulmonary presentations

The distinction between amyloidosis and neurofibromatosis type 1 can be made by the history and the clinical examination. However, a  definitive diagnosis of amyloidosis or light chain deposition disease requires tissue examination for the presence or absence of amyloid fibrils.

Cautery and radiofrequency ablation (RFA) devices are commonly used in shoulder arthroscopic surgery for hemostasis and ablation of soft tissue. Although these devices are easily used and applied, complications (eg, extensive release of deltoid muscle,¹ nerve damage,² tendon damage,³ cartilage damage from heat transfer⁴) can occur during arthroscopic surgery. Radiofrequency devices can elevate fluid temperatures to unsafe levels and directly or indirectly injure surrounding tissue.^5,6 Skin complications from using these devices include direct burns to the subcutaneous tissues from the joint to the skin surface⁷ and skin burns related to overheated arthroscopic fluid.⁸

In our English-language literature review, however, we found no report of a skin burn secondary to contact between a RFA device and a spinal needle used in identifying structures during an arthroscopic acromioplasty. We report such a case here. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 51-year-old woman injured her left, nondominant shoulder when a descending garage door hit her directly on the superior aspect of the shoulder. She had immediate onset of pain on the top and lateral side of the shoulder and was evaluated by a primary care physician. Radiographs and magnetic resonance imaging (MRI) were normal. The patient was referred to an orthopedic surgeon for further evaluation.

The orthopedic surgeon found her to be in good health, with no history of diabetes, vascular conditions, or skin disorders. The initial diagnosis after history taking and physical examination was impingement syndrome with subacromial bursitis. The surgeon recommended nonoperative treatment: ice, nonsteroidal anti-inflammatory drugs, and physical therapy. After 3 months, the patient’s examination was unchanged, and there was no improvement in pain. Cortisone injected into the subacromial space helped for a few weeks, but the pain returned. After 2 more cortisone injections over 9 months failed, repeat MRI showed no tears of the rotator cuff or any other salient abnormalities. The treatment options were discussed with the patient, and, because the physical examination findings were consistent with impingement syndrome and nonoperative measures had failed, she consented to arthroscopic evaluation of the shoulder and arthroscopic partial anterior-lateral acromioplasty.

The procedure was performed 8 months after initial injury. With the patient under general anesthesia and in a lateral decubitus position, her arm was placed in an arm holder. Before the partial acromioplasty, two 18-gauge spinal needles were inserted from the skin surface into the subacromial space to help localize the anterolateral acromion and the acromioclavicular joint. The procedure was performed with a pump using saline bags kept at room temperature. A bipolar radiofrequency device (Stryker Energy Radiofrequency Ablation System; Stryker, Mahwah, New Jersey) was used to débride the subacromial bursa and the periosteum of the undersurface of the acromion. While the bursa was being débrided, the radiofrequency device inadvertently touched the anterior lateral needle probe, and a small skin burn formed around the needle on the surface of the shoulder (Figure). The radiofrequency device did not directly contact the skin, and the deltoid fascia was intact. The spinal needle was removed, and the skin around the burn was excised; the muscle beneath the skin was intact and showed no signs of thermal damage. The skin was mobilized and closed with interrupted simple sutures using a 4-0 nylon suture. The procedure was then completed with no other complications.

After surgery, the patient recovered without complications, and the skin lesion healed with no signs of infection and no skin or muscle defects. Some stiffness was treated with medication and physical therapy. Nine months after surgery, the patient reported mild shoulder stiffness and remained dissatisfied with the appearance of the skin in the area of the burn.

Discussion

Our patient’s case is a reminder that contact between a radiofrequency device and metal needles can transfer heat to tissues and cause skin burns. When using a radiofrequency device around metal needles or cannulas, surgeons should be sure to avoid prolonged contact with the metal. Our patient’s case is the first reported case of a thermal skin injury occurring when a spinal needle was heated by an arthroscopic ablater.

Other authors have reported indirect thermal skin injuries caused by radiofrequency devices during arthroscopic surgery, but the causes were postulated to be direct contact between device and skin⁷ and overheating of the arthroscopy fluid.^5,6,8 Huang and colleagues⁸ reported that full-thickness skin burns occurred when normal saline used during routine knee arthroscopy overheated from use of a radiofrequency device. Burn lesions, noted on their patient’s leg within 1 day after surgery, required subsequent débridement, a muscle flap, and split-skin grafting. Skin burns caused by overheated fluid have occurred irrespective of type of fluid used (eg, 1.5% glycine or lactated Ringer solution).⁶ There was no evidence that our patient’s burn resulted from extravasated overheated fluid, as the lesion was localized to the area immediately around the needle and was not geographic, as was described by Huang and colleagues.⁸

Other possible causes of skin burns during arthroscopic surgery have been described, but none applies in our patient’s case. Segami and colleagues⁷ described a burn resulting from direct transfer of heat from the radiofrequency device to the skin because of their proximity. This mechanism was not the cause in our patient’s case; there was no evidence of a defect or burned deltoid muscle at time of surgery. Lau and Dao⁹ reported 2 small full-thickness skin burns caused by a fiberoptic-light cable tip placed on a patient’s leg; in addition, the hot (>170°C) cables caused the paper drapes to combust.⁹ Skin burns secondary to use of skin antiseptics have been reported,¹⁰ but such lesions typically are located beneath tourniquets or in areas of friction from surgical drapes. In some cases, lesions described as skin burns may actually have been pressure lesions secondary to moist skin and friction.¹¹

Whether type of radiofrequency device contributes to the occurrence of heat-related lesions during arthroscopic surgery is unknown. Some investigators have suggested there is more potential for harm with bipolar RFA devices than with monopolar devices.^12,13 Monopolar devices pass energy between a probe and a grounding plate, whereas bipolar devices pass energy through 2 points on the probe.¹⁴ Because the heat for the monopolar probe derives from the frictional resistance of tissues to each other rather than from the probe itself, the bipolar probe theoretically allows for better temperature control. In addition, bipolar probes require less current to achieve the same heating effect. However, recent studies have suggested that, compared with monopolar radiofrequency devices, bipolar radiofrequency devices are associated with larger increases in temperature at equal depths after an equal number of applications.^12,13

To our knowledge, no one has specifically investigated the type of bipolar device used in the present case. This case report, the first to describe a thermal skin injury caused by direct contact between a radiofrequency device and a metal needle inserted in the skin, is a reminder that contact between radiofrequency devices and spinal needles or other metal cannulas used in arthroscopic surgery should be avoided.

Cautery and radiofrequency ablation (RFA) devices are commonly used in shoulder arthroscopic surgery for hemostasis and ablation of soft tissue. Although these devices are easily used and applied, complications (eg, extensive release of deltoid muscle,¹ nerve damage,² tendon damage,³ cartilage damage from heat transfer⁴) can occur during arthroscopic surgery. Radiofrequency devices can elevate fluid temperatures to unsafe levels and directly or indirectly injure surrounding tissue.^5,6 Skin complications from using these devices include direct burns to the subcutaneous tissues from the joint to the skin surface⁷ and skin burns related to overheated arthroscopic fluid.⁸

In our English-language literature review, however, we found no report of a skin burn secondary to contact between a RFA device and a spinal needle used in identifying structures during an arthroscopic acromioplasty. We report such a case here. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 51-year-old woman injured her left, nondominant shoulder when a descending garage door hit her directly on the superior aspect of the shoulder. She had immediate onset of pain on the top and lateral side of the shoulder and was evaluated by a primary care physician. Radiographs and magnetic resonance imaging (MRI) were normal. The patient was referred to an orthopedic surgeon for further evaluation.

The orthopedic surgeon found her to be in good health, with no history of diabetes, vascular conditions, or skin disorders. The initial diagnosis after history taking and physical examination was impingement syndrome with subacromial bursitis. The surgeon recommended nonoperative treatment: ice, nonsteroidal anti-inflammatory drugs, and physical therapy. After 3 months, the patient’s examination was unchanged, and there was no improvement in pain. Cortisone injected into the subacromial space helped for a few weeks, but the pain returned. After 2 more cortisone injections over 9 months failed, repeat MRI showed no tears of the rotator cuff or any other salient abnormalities. The treatment options were discussed with the patient, and, because the physical examination findings were consistent with impingement syndrome and nonoperative measures had failed, she consented to arthroscopic evaluation of the shoulder and arthroscopic partial anterior-lateral acromioplasty.

The procedure was performed 8 months after initial injury. With the patient under general anesthesia and in a lateral decubitus position, her arm was placed in an arm holder. Before the partial acromioplasty, two 18-gauge spinal needles were inserted from the skin surface into the subacromial space to help localize the anterolateral acromion and the acromioclavicular joint. The procedure was performed with a pump using saline bags kept at room temperature. A bipolar radiofrequency device (Stryker Energy Radiofrequency Ablation System; Stryker, Mahwah, New Jersey) was used to débride the subacromial bursa and the periosteum of the undersurface of the acromion. While the bursa was being débrided, the radiofrequency device inadvertently touched the anterior lateral needle probe, and a small skin burn formed around the needle on the surface of the shoulder (Figure). The radiofrequency device did not directly contact the skin, and the deltoid fascia was intact. The spinal needle was removed, and the skin around the burn was excised; the muscle beneath the skin was intact and showed no signs of thermal damage. The skin was mobilized and closed with interrupted simple sutures using a 4-0 nylon suture. The procedure was then completed with no other complications.

After surgery, the patient recovered without complications, and the skin lesion healed with no signs of infection and no skin or muscle defects. Some stiffness was treated with medication and physical therapy. Nine months after surgery, the patient reported mild shoulder stiffness and remained dissatisfied with the appearance of the skin in the area of the burn.

Discussion

Our patient’s case is a reminder that contact between a radiofrequency device and metal needles can transfer heat to tissues and cause skin burns. When using a radiofrequency device around metal needles or cannulas, surgeons should be sure to avoid prolonged contact with the metal. Our patient’s case is the first reported case of a thermal skin injury occurring when a spinal needle was heated by an arthroscopic ablater.

Other authors have reported indirect thermal skin injuries caused by radiofrequency devices during arthroscopic surgery, but the causes were postulated to be direct contact between device and skin⁷ and overheating of the arthroscopy fluid.^5,6,8 Huang and colleagues⁸ reported that full-thickness skin burns occurred when normal saline used during routine knee arthroscopy overheated from use of a radiofrequency device. Burn lesions, noted on their patient’s leg within 1 day after surgery, required subsequent débridement, a muscle flap, and split-skin grafting. Skin burns caused by overheated fluid have occurred irrespective of type of fluid used (eg, 1.5% glycine or lactated Ringer solution).⁶ There was no evidence that our patient’s burn resulted from extravasated overheated fluid, as the lesion was localized to the area immediately around the needle and was not geographic, as was described by Huang and colleagues.⁸

Other possible causes of skin burns during arthroscopic surgery have been described, but none applies in our patient’s case. Segami and colleagues⁷ described a burn resulting from direct transfer of heat from the radiofrequency device to the skin because of their proximity. This mechanism was not the cause in our patient’s case; there was no evidence of a defect or burned deltoid muscle at time of surgery. Lau and Dao⁹ reported 2 small full-thickness skin burns caused by a fiberoptic-light cable tip placed on a patient’s leg; in addition, the hot (>170°C) cables caused the paper drapes to combust.⁹ Skin burns secondary to use of skin antiseptics have been reported,¹⁰ but such lesions typically are located beneath tourniquets or in areas of friction from surgical drapes. In some cases, lesions described as skin burns may actually have been pressure lesions secondary to moist skin and friction.¹¹

Whether type of radiofrequency device contributes to the occurrence of heat-related lesions during arthroscopic surgery is unknown. Some investigators have suggested there is more potential for harm with bipolar RFA devices than with monopolar devices.^12,13 Monopolar devices pass energy between a probe and a grounding plate, whereas bipolar devices pass energy through 2 points on the probe.¹⁴ Because the heat for the monopolar probe derives from the frictional resistance of tissues to each other rather than from the probe itself, the bipolar probe theoretically allows for better temperature control. In addition, bipolar probes require less current to achieve the same heating effect. However, recent studies have suggested that, compared with monopolar radiofrequency devices, bipolar radiofrequency devices are associated with larger increases in temperature at equal depths after an equal number of applications.^12,13

To our knowledge, no one has specifically investigated the type of bipolar device used in the present case. This case report, the first to describe a thermal skin injury caused by direct contact between a radiofrequency device and a metal needle inserted in the skin, is a reminder that contact between radiofrequency devices and spinal needles or other metal cannulas used in arthroscopic surgery should be avoided.

Cautery and radiofrequency ablation (RFA) devices are commonly used in shoulder arthroscopic surgery for hemostasis and ablation of soft tissue. Although these devices are easily used and applied, complications (eg, extensive release of deltoid muscle,¹ nerve damage,² tendon damage,³ cartilage damage from heat transfer⁴) can occur during arthroscopic surgery. Radiofrequency devices can elevate fluid temperatures to unsafe levels and directly or indirectly injure surrounding tissue.^5,6 Skin complications from using these devices include direct burns to the subcutaneous tissues from the joint to the skin surface⁷ and skin burns related to overheated arthroscopic fluid.⁸

In our English-language literature review, however, we found no report of a skin burn secondary to contact between a RFA device and a spinal needle used in identifying structures during an arthroscopic acromioplasty. We report such a case here. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 51-year-old woman injured her left, nondominant shoulder when a descending garage door hit her directly on the superior aspect of the shoulder. She had immediate onset of pain on the top and lateral side of the shoulder and was evaluated by a primary care physician. Radiographs and magnetic resonance imaging (MRI) were normal. The patient was referred to an orthopedic surgeon for further evaluation.

The orthopedic surgeon found her to be in good health, with no history of diabetes, vascular conditions, or skin disorders. The initial diagnosis after history taking and physical examination was impingement syndrome with subacromial bursitis. The surgeon recommended nonoperative treatment: ice, nonsteroidal anti-inflammatory drugs, and physical therapy. After 3 months, the patient’s examination was unchanged, and there was no improvement in pain. Cortisone injected into the subacromial space helped for a few weeks, but the pain returned. After 2 more cortisone injections over 9 months failed, repeat MRI showed no tears of the rotator cuff or any other salient abnormalities. The treatment options were discussed with the patient, and, because the physical examination findings were consistent with impingement syndrome and nonoperative measures had failed, she consented to arthroscopic evaluation of the shoulder and arthroscopic partial anterior-lateral acromioplasty.

The procedure was performed 8 months after initial injury. With the patient under general anesthesia and in a lateral decubitus position, her arm was placed in an arm holder. Before the partial acromioplasty, two 18-gauge spinal needles were inserted from the skin surface into the subacromial space to help localize the anterolateral acromion and the acromioclavicular joint. The procedure was performed with a pump using saline bags kept at room temperature. A bipolar radiofrequency device (Stryker Energy Radiofrequency Ablation System; Stryker, Mahwah, New Jersey) was used to débride the subacromial bursa and the periosteum of the undersurface of the acromion. While the bursa was being débrided, the radiofrequency device inadvertently touched the anterior lateral needle probe, and a small skin burn formed around the needle on the surface of the shoulder (Figure). The radiofrequency device did not directly contact the skin, and the deltoid fascia was intact. The spinal needle was removed, and the skin around the burn was excised; the muscle beneath the skin was intact and showed no signs of thermal damage. The skin was mobilized and closed with interrupted simple sutures using a 4-0 nylon suture. The procedure was then completed with no other complications.

After surgery, the patient recovered without complications, and the skin lesion healed with no signs of infection and no skin or muscle defects. Some stiffness was treated with medication and physical therapy. Nine months after surgery, the patient reported mild shoulder stiffness and remained dissatisfied with the appearance of the skin in the area of the burn.

Discussion

Our patient’s case is a reminder that contact between a radiofrequency device and metal needles can transfer heat to tissues and cause skin burns. When using a radiofrequency device around metal needles or cannulas, surgeons should be sure to avoid prolonged contact with the metal. Our patient’s case is the first reported case of a thermal skin injury occurring when a spinal needle was heated by an arthroscopic ablater.

Other authors have reported indirect thermal skin injuries caused by radiofrequency devices during arthroscopic surgery, but the causes were postulated to be direct contact between device and skin⁷ and overheating of the arthroscopy fluid.^5,6,8 Huang and colleagues⁸ reported that full-thickness skin burns occurred when normal saline used during routine knee arthroscopy overheated from use of a radiofrequency device. Burn lesions, noted on their patient’s leg within 1 day after surgery, required subsequent débridement, a muscle flap, and split-skin grafting. Skin burns caused by overheated fluid have occurred irrespective of type of fluid used (eg, 1.5% glycine or lactated Ringer solution).⁶ There was no evidence that our patient’s burn resulted from extravasated overheated fluid, as the lesion was localized to the area immediately around the needle and was not geographic, as was described by Huang and colleagues.⁸

Other possible causes of skin burns during arthroscopic surgery have been described, but none applies in our patient’s case. Segami and colleagues⁷ described a burn resulting from direct transfer of heat from the radiofrequency device to the skin because of their proximity. This mechanism was not the cause in our patient’s case; there was no evidence of a defect or burned deltoid muscle at time of surgery. Lau and Dao⁹ reported 2 small full-thickness skin burns caused by a fiberoptic-light cable tip placed on a patient’s leg; in addition, the hot (>170°C) cables caused the paper drapes to combust.⁹ Skin burns secondary to use of skin antiseptics have been reported,¹⁰ but such lesions typically are located beneath tourniquets or in areas of friction from surgical drapes. In some cases, lesions described as skin burns may actually have been pressure lesions secondary to moist skin and friction.¹¹

Whether type of radiofrequency device contributes to the occurrence of heat-related lesions during arthroscopic surgery is unknown. Some investigators have suggested there is more potential for harm with bipolar RFA devices than with monopolar devices.^12,13 Monopolar devices pass energy between a probe and a grounding plate, whereas bipolar devices pass energy through 2 points on the probe.¹⁴ Because the heat for the monopolar probe derives from the frictional resistance of tissues to each other rather than from the probe itself, the bipolar probe theoretically allows for better temperature control. In addition, bipolar probes require less current to achieve the same heating effect. However, recent studies have suggested that, compared with monopolar radiofrequency devices, bipolar radiofrequency devices are associated with larger increases in temperature at equal depths after an equal number of applications.^12,13

To our knowledge, no one has specifically investigated the type of bipolar device used in the present case. This case report, the first to describe a thermal skin injury caused by direct contact between a radiofrequency device and a metal needle inserted in the skin, is a reminder that contact between radiofrequency devices and spinal needles or other metal cannulas used in arthroscopic surgery should be avoided.

The accuracy of using computed tomography (CT) to assess lumbar interbody fusion with titanium implants has been questioned in the past.^1-4 Reports have most often focused on older technologies using paired, threaded, smooth-surface titanium devices. Some authors have reported they could not confidently assess the quality of fusions using CT because of implant artifact.^1-3

When pseudarthrosis is suspected clinically, and imaging results are inconclusive, surgical explorations may be performed with mechanical stressing of the segment to assess for motion.^2,5-7 However, surgical exploration not only has the morbidity of another surgery but may not be conclusive. Direct exploration of an interbody fusion is problematic. In some cases, there may be residual normal springing motion through posterior elements, even in the presence of a solid interbody fusion, which can be confusing.⁵ Radiologic confirmation of fusion status is therefore preferred over surgical exploration. CT is the imaging modality used most often to assess spinal fusions.^8,9

A new titanium interbody fusion implant (Endoskeleton TA; Titan Spine, Mequon, Wisconsin) preserves the endplate and has an acid-etched titanium surface for osseous integration and a wide central aperture for bone graft (Figure 1). Compared with earlier titanium implants, this design may allow for more accurate CT imaging and fusion assessment. We conducted a study to determine the interobserver reliability of using CT to evaluate bone formation and other radiographic variables with this new titanium interbody device.

Materials and Methods

After receiving institutional review board approval for this study, as well as patient consent, we obtained and analyzed CT scans of patients after they had undergone anterior lumbar interbody fusion (ALIF) at L3–S1 as part of a separate clinical outcomes study.

Each patient received an Endoskeleton TA implant. The fusion cage was packed with 2 sponges (3.0 mg per fusion level) of bone morphogenetic protein, or BMP (InFuse; Medtronic, Minneapolis, Minnesota). In addition, 1 to 3 cm³ of hydroxyapatite/β-‌tricalcium phosphate (MasterGraft, Medtronic) collagen sponge was used as graft extender to fill any remaining gaps within the cage. Pedicle screw fixation was used in all cases.

Patients were randomly assigned to have fine-cut CT scans with reconstructed images at 6, 9, or 12 months. The scans were reviewed by 2 independent radiologists who were blinded to each other’s interpretations and the clinical results. The radiographic fusion criteria are listed in Tables 1 to 3. Interobserver agreement (κ) was calculated separately for each radiographic criterion and could range from 0.00 (no agreement) to 1.00 (perfect agreement).^10,11

Results

The study involved 33 patients (17 men, 16 women) with 56 lumbar spinal fusion levels. Mean age was 46 years (range, 23-66 years). Six patients (18%) were nicotine users. Seventeen patients were scanned at 6 months, 9 at 9 months, and 7 at 12 months. There were no significant differences in results between men and women, between nicotine users and nonusers, or among patients evaluated at 6, 9, or 12 months.

The radiologists agreed on 345 of the 392 data points reviewed (κ = 0.88). Interobserver agreement results for the fusion criteria are listed in Tables 1 and 3. Interobserver agreement was 0.77 for overall fusion grade, with the radiologists noting definite fusion (grade 5) in 80% and 91% of the levels (Table 1). Other radiographic criteria are listed in Tables 2 and 3. Interobserver agreement was 0.80 for degree of artifact, 0.95 for subsidence, 0.96 for both lucency and trabecular bone, 0.77 for anterior osseous bridging, and 0.95 for cystic vertebral changes.

Discussion

Radiographic analysis of interbody fusions is an important clinical issue. Investigators have shown that CT is the radiographic method of choice for assessing fusion.^8,9 Others have reported that assessing fusion with metallic interbody implants is more difficult compared with PEEK (polyether ether ketone) or allograft bone.^3,4,5,12

Heithoff and colleagues^1,2 reported on difficulties they encountered in assessing interbody fusion with titanium implants, and their research has often been cited. The authors concluded that they could not accurately assess fusion in these cases because of artifact from the small apertures in the cages and metallic scatter. Their study was very small (8 patients, 12 surgical levels) and used paired BAK (Bagby and Kuslich) cages (Zimmer, Warsaw, Indiana).

Recently, a unique surface technology, used to manufacture osseointegrative dental implants, has been adapted for use in the spine.^13-15 Acid etching modifies the surface of titanium to create a nano-scale (micron-level) alteration. Compared with PEEK and smooth titanium, acid-etched titanium stimulates a better osteogenic environment.^16,17 As this technology is now used clinically in spinal surgery, we thought it important to revisit the issue of CT analysis for fusion assessment with the newer titanium implants.

Artifact

The results of our study support the idea that the design of a titanium interbody fusion implant is important to radiographic analysis. The implant studied has a large open central aperture that appears to generate less artifact than historical controls (paired cylindrical cages) have.^1-4 Other investigators have reported fewer problems with artifact in their studies of implants incorporating larger openings for bone graft.^6,18 The radiologists in the present study found no significant problems with artifact. Less artifact is clinically important, as the remaining fusion variables can be more clearly visualized (Table 2, Figure 2).

Anterior Osseous Bridging, Subsidence, Lysis

In this study, the bony endplates were preserved. The disc and endplate cartilage was removed without reaming or drilling. Endplate reaming most likely contributes to subsidence and loss of original fixation between implant and bone interface.^1,4,12 Some authors have advocated recessing the cages deeply and then packing bone anteriorly to create a “sentinel fusion sign.”^1,2,6 Deeply seating interbody implants, instead of resting them more widely on the apophyseal ring of the vertebral endplate, may also lead to subsidence.^4,12 The issue of identifying a sentinel fusion sign is relevant only if the surgeon tries to create one. In the present study, the implant used was an impacted cage positioned on the apophyseal perimeter of the disc space, just slightly recessed, so there was no attempt to create a sentinel fusion sign, as reflected in the relatively low scores on anterior osseous bridging (48%, 52%).

Subsidence and peri-implant lysis are pathologic variables associated with motion and bone loss. Sethi and colleagues¹⁹ noted a high percentage of endplate resorption and subsidence in cases reviewed using PEEK or allograft spacers paired with BMP-2. Although BMP-2 was used in the present study, we found very low rates of subsidence (0%, 5%) and no significant peri-implant lucencies (2%, 4%) (Figure 2). Interobserver agreement for these variables was high (0.95, 0.96). We hypothesize that the combination of endplate-sparing surgical technique and implant–bone integration contributed to these results.

Trabecular Bone and Fusion Grade

The primary radiographic criterion for solid interbody fusion is trabecular bone throughout the cage, bridging the vertebral bodies. In our study, the success rates for this variable were 96% and 100%, and there was very high interobserver agreement (0.96) (Figure 3). This very high fusion rate may preclude detecting subtle differences in interobserver agreement, but to what degree, if any, is unknown. Other investigators have effectively identified trabecular bone across the interspace and throughout the cages.^6,18 The openings for bone formation were larger in the implants they used than in first-generation fusion cages but not as large as the implant openings in the present study. Larger openings may correlate with improved ability to visualize bridging bone on CT.

Radiologists and surgeons must ultimately arrive at a conclusion regarding the likelihood a fusion has occurred. Our radiologists integrated all the separate radiologic variables cited here, as well as their overall impressions of the scans, to arrive at a final grade regarding fusion quality (Figures 3, 4). Although this category provides the most interpretive latitude of all the variables examined, the results demonstrate high interobserver reliability. Agreement to exactly the same fusion grade was 0.77, and agreement to within 1 category grade was 0.95.

This study had several limitations. Surgical explorations were not clinically indicated and were not performed. There were no suspected nonunions or hardware complications, two of the most common indications for exploration. In addition, this study was conducted not to determine specific accuracy of CT (compared with surgery exploration) for fusion assessment but to assess interobserver reliability. The clinical success rates for this population were high, and no patient required revision surgery for suspected pseudarthrosis. To assess the true accuracy of CT for fusion assessment, one would have to subject patients to follow-up exploratory surgery to test fusions mechanically.

Another limitation is the lack of a single industry-accepted radiographic fusion grading system. Fusion criteria are not standardized across all studies. Our radiologists have extensive research experience and limit their practices to neuromuscular radiology with a concentration on the spine. The radiographic criteria cited here are the same criteria they use in clinical practice, when reviewing CT scans for clinicians. Last, there was no control group for direct comparison against other cages. Historical controls were cited. This does not adversely affect the conclusions of this investigation.

Conclusion

Clinicians have been reluctant to rely on CT with titanium devices because of concerns about the accuracy of image interpretations. The interbody device used in this study demonstrated minimal artifact and minimal subsidence, and trabecular bone was easily identified throughout the implant in the majority of cases reviewed. We found high interobserver agreement scores across all fusion criteria. Although surgical exploration remains the gold standard for fusion assessment, surgeons should have confidence in using CT with this titanium implant.

The accuracy of using computed tomography (CT) to assess lumbar interbody fusion with titanium implants has been questioned in the past.^1-4 Reports have most often focused on older technologies using paired, threaded, smooth-surface titanium devices. Some authors have reported they could not confidently assess the quality of fusions using CT because of implant artifact.^1-3

When pseudarthrosis is suspected clinically, and imaging results are inconclusive, surgical explorations may be performed with mechanical stressing of the segment to assess for motion.^2,5-7 However, surgical exploration not only has the morbidity of another surgery but may not be conclusive. Direct exploration of an interbody fusion is problematic. In some cases, there may be residual normal springing motion through posterior elements, even in the presence of a solid interbody fusion, which can be confusing.⁵ Radiologic confirmation of fusion status is therefore preferred over surgical exploration. CT is the imaging modality used most often to assess spinal fusions.^8,9

A new titanium interbody fusion implant (Endoskeleton TA; Titan Spine, Mequon, Wisconsin) preserves the endplate and has an acid-etched titanium surface for osseous integration and a wide central aperture for bone graft (Figure 1). Compared with earlier titanium implants, this design may allow for more accurate CT imaging and fusion assessment. We conducted a study to determine the interobserver reliability of using CT to evaluate bone formation and other radiographic variables with this new titanium interbody device.

Materials and Methods

After receiving institutional review board approval for this study, as well as patient consent, we obtained and analyzed CT scans of patients after they had undergone anterior lumbar interbody fusion (ALIF) at L3–S1 as part of a separate clinical outcomes study.

Each patient received an Endoskeleton TA implant. The fusion cage was packed with 2 sponges (3.0 mg per fusion level) of bone morphogenetic protein, or BMP (InFuse; Medtronic, Minneapolis, Minnesota). In addition, 1 to 3 cm³ of hydroxyapatite/β-‌tricalcium phosphate (MasterGraft, Medtronic) collagen sponge was used as graft extender to fill any remaining gaps within the cage. Pedicle screw fixation was used in all cases.

Patients were randomly assigned to have fine-cut CT scans with reconstructed images at 6, 9, or 12 months. The scans were reviewed by 2 independent radiologists who were blinded to each other’s interpretations and the clinical results. The radiographic fusion criteria are listed in Tables 1 to 3. Interobserver agreement (κ) was calculated separately for each radiographic criterion and could range from 0.00 (no agreement) to 1.00 (perfect agreement).^10,11

Results

The study involved 33 patients (17 men, 16 women) with 56 lumbar spinal fusion levels. Mean age was 46 years (range, 23-66 years). Six patients (18%) were nicotine users. Seventeen patients were scanned at 6 months, 9 at 9 months, and 7 at 12 months. There were no significant differences in results between men and women, between nicotine users and nonusers, or among patients evaluated at 6, 9, or 12 months.

The radiologists agreed on 345 of the 392 data points reviewed (κ = 0.88). Interobserver agreement results for the fusion criteria are listed in Tables 1 and 3. Interobserver agreement was 0.77 for overall fusion grade, with the radiologists noting definite fusion (grade 5) in 80% and 91% of the levels (Table 1). Other radiographic criteria are listed in Tables 2 and 3. Interobserver agreement was 0.80 for degree of artifact, 0.95 for subsidence, 0.96 for both lucency and trabecular bone, 0.77 for anterior osseous bridging, and 0.95 for cystic vertebral changes.

Discussion

Radiographic analysis of interbody fusions is an important clinical issue. Investigators have shown that CT is the radiographic method of choice for assessing fusion.^8,9 Others have reported that assessing fusion with metallic interbody implants is more difficult compared with PEEK (polyether ether ketone) or allograft bone.^3,4,5,12

Heithoff and colleagues^1,2 reported on difficulties they encountered in assessing interbody fusion with titanium implants, and their research has often been cited. The authors concluded that they could not accurately assess fusion in these cases because of artifact from the small apertures in the cages and metallic scatter. Their study was very small (8 patients, 12 surgical levels) and used paired BAK (Bagby and Kuslich) cages (Zimmer, Warsaw, Indiana).

Recently, a unique surface technology, used to manufacture osseointegrative dental implants, has been adapted for use in the spine.^13-15 Acid etching modifies the surface of titanium to create a nano-scale (micron-level) alteration. Compared with PEEK and smooth titanium, acid-etched titanium stimulates a better osteogenic environment.^16,17 As this technology is now used clinically in spinal surgery, we thought it important to revisit the issue of CT analysis for fusion assessment with the newer titanium implants.

Artifact

The results of our study support the idea that the design of a titanium interbody fusion implant is important to radiographic analysis. The implant studied has a large open central aperture that appears to generate less artifact than historical controls (paired cylindrical cages) have.^1-4 Other investigators have reported fewer problems with artifact in their studies of implants incorporating larger openings for bone graft.^6,18 The radiologists in the present study found no significant problems with artifact. Less artifact is clinically important, as the remaining fusion variables can be more clearly visualized (Table 2, Figure 2).

Anterior Osseous Bridging, Subsidence, Lysis

In this study, the bony endplates were preserved. The disc and endplate cartilage was removed without reaming or drilling. Endplate reaming most likely contributes to subsidence and loss of original fixation between implant and bone interface.^1,4,12 Some authors have advocated recessing the cages deeply and then packing bone anteriorly to create a “sentinel fusion sign.”^1,2,6 Deeply seating interbody implants, instead of resting them more widely on the apophyseal ring of the vertebral endplate, may also lead to subsidence.^4,12 The issue of identifying a sentinel fusion sign is relevant only if the surgeon tries to create one. In the present study, the implant used was an impacted cage positioned on the apophyseal perimeter of the disc space, just slightly recessed, so there was no attempt to create a sentinel fusion sign, as reflected in the relatively low scores on anterior osseous bridging (48%, 52%).

Subsidence and peri-implant lysis are pathologic variables associated with motion and bone loss. Sethi and colleagues¹⁹ noted a high percentage of endplate resorption and subsidence in cases reviewed using PEEK or allograft spacers paired with BMP-2. Although BMP-2 was used in the present study, we found very low rates of subsidence (0%, 5%) and no significant peri-implant lucencies (2%, 4%) (Figure 2). Interobserver agreement for these variables was high (0.95, 0.96). We hypothesize that the combination of endplate-sparing surgical technique and implant–bone integration contributed to these results.

Trabecular Bone and Fusion Grade

The primary radiographic criterion for solid interbody fusion is trabecular bone throughout the cage, bridging the vertebral bodies. In our study, the success rates for this variable were 96% and 100%, and there was very high interobserver agreement (0.96) (Figure 3). This very high fusion rate may preclude detecting subtle differences in interobserver agreement, but to what degree, if any, is unknown. Other investigators have effectively identified trabecular bone across the interspace and throughout the cages.^6,18 The openings for bone formation were larger in the implants they used than in first-generation fusion cages but not as large as the implant openings in the present study. Larger openings may correlate with improved ability to visualize bridging bone on CT.

Radiologists and surgeons must ultimately arrive at a conclusion regarding the likelihood a fusion has occurred. Our radiologists integrated all the separate radiologic variables cited here, as well as their overall impressions of the scans, to arrive at a final grade regarding fusion quality (Figures 3, 4). Although this category provides the most interpretive latitude of all the variables examined, the results demonstrate high interobserver reliability. Agreement to exactly the same fusion grade was 0.77, and agreement to within 1 category grade was 0.95.

This study had several limitations. Surgical explorations were not clinically indicated and were not performed. There were no suspected nonunions or hardware complications, two of the most common indications for exploration. In addition, this study was conducted not to determine specific accuracy of CT (compared with surgery exploration) for fusion assessment but to assess interobserver reliability. The clinical success rates for this population were high, and no patient required revision surgery for suspected pseudarthrosis. To assess the true accuracy of CT for fusion assessment, one would have to subject patients to follow-up exploratory surgery to test fusions mechanically.

Another limitation is the lack of a single industry-accepted radiographic fusion grading system. Fusion criteria are not standardized across all studies. Our radiologists have extensive research experience and limit their practices to neuromuscular radiology with a concentration on the spine. The radiographic criteria cited here are the same criteria they use in clinical practice, when reviewing CT scans for clinicians. Last, there was no control group for direct comparison against other cages. Historical controls were cited. This does not adversely affect the conclusions of this investigation.

Conclusion

Clinicians have been reluctant to rely on CT with titanium devices because of concerns about the accuracy of image interpretations. The interbody device used in this study demonstrated minimal artifact and minimal subsidence, and trabecular bone was easily identified throughout the implant in the majority of cases reviewed. We found high interobserver agreement scores across all fusion criteria. Although surgical exploration remains the gold standard for fusion assessment, surgeons should have confidence in using CT with this titanium implant.

The accuracy of using computed tomography (CT) to assess lumbar interbody fusion with titanium implants has been questioned in the past.^1-4 Reports have most often focused on older technologies using paired, threaded, smooth-surface titanium devices. Some authors have reported they could not confidently assess the quality of fusions using CT because of implant artifact.^1-3

When pseudarthrosis is suspected clinically, and imaging results are inconclusive, surgical explorations may be performed with mechanical stressing of the segment to assess for motion.^2,5-7 However, surgical exploration not only has the morbidity of another surgery but may not be conclusive. Direct exploration of an interbody fusion is problematic. In some cases, there may be residual normal springing motion through posterior elements, even in the presence of a solid interbody fusion, which can be confusing.⁵ Radiologic confirmation of fusion status is therefore preferred over surgical exploration. CT is the imaging modality used most often to assess spinal fusions.^8,9

A new titanium interbody fusion implant (Endoskeleton TA; Titan Spine, Mequon, Wisconsin) preserves the endplate and has an acid-etched titanium surface for osseous integration and a wide central aperture for bone graft (Figure 1). Compared with earlier titanium implants, this design may allow for more accurate CT imaging and fusion assessment. We conducted a study to determine the interobserver reliability of using CT to evaluate bone formation and other radiographic variables with this new titanium interbody device.

Materials and Methods

After receiving institutional review board approval for this study, as well as patient consent, we obtained and analyzed CT scans of patients after they had undergone anterior lumbar interbody fusion (ALIF) at L3–S1 as part of a separate clinical outcomes study.

Each patient received an Endoskeleton TA implant. The fusion cage was packed with 2 sponges (3.0 mg per fusion level) of bone morphogenetic protein, or BMP (InFuse; Medtronic, Minneapolis, Minnesota). In addition, 1 to 3 cm³ of hydroxyapatite/β-‌tricalcium phosphate (MasterGraft, Medtronic) collagen sponge was used as graft extender to fill any remaining gaps within the cage. Pedicle screw fixation was used in all cases.

Patients were randomly assigned to have fine-cut CT scans with reconstructed images at 6, 9, or 12 months. The scans were reviewed by 2 independent radiologists who were blinded to each other’s interpretations and the clinical results. The radiographic fusion criteria are listed in Tables 1 to 3. Interobserver agreement (κ) was calculated separately for each radiographic criterion and could range from 0.00 (no agreement) to 1.00 (perfect agreement).^10,11

Results

The study involved 33 patients (17 men, 16 women) with 56 lumbar spinal fusion levels. Mean age was 46 years (range, 23-66 years). Six patients (18%) were nicotine users. Seventeen patients were scanned at 6 months, 9 at 9 months, and 7 at 12 months. There were no significant differences in results between men and women, between nicotine users and nonusers, or among patients evaluated at 6, 9, or 12 months.

The radiologists agreed on 345 of the 392 data points reviewed (κ = 0.88). Interobserver agreement results for the fusion criteria are listed in Tables 1 and 3. Interobserver agreement was 0.77 for overall fusion grade, with the radiologists noting definite fusion (grade 5) in 80% and 91% of the levels (Table 1). Other radiographic criteria are listed in Tables 2 and 3. Interobserver agreement was 0.80 for degree of artifact, 0.95 for subsidence, 0.96 for both lucency and trabecular bone, 0.77 for anterior osseous bridging, and 0.95 for cystic vertebral changes.

Discussion

Radiographic analysis of interbody fusions is an important clinical issue. Investigators have shown that CT is the radiographic method of choice for assessing fusion.^8,9 Others have reported that assessing fusion with metallic interbody implants is more difficult compared with PEEK (polyether ether ketone) or allograft bone.^3,4,5,12

Heithoff and colleagues^1,2 reported on difficulties they encountered in assessing interbody fusion with titanium implants, and their research has often been cited. The authors concluded that they could not accurately assess fusion in these cases because of artifact from the small apertures in the cages and metallic scatter. Their study was very small (8 patients, 12 surgical levels) and used paired BAK (Bagby and Kuslich) cages (Zimmer, Warsaw, Indiana).

Recently, a unique surface technology, used to manufacture osseointegrative dental implants, has been adapted for use in the spine.^13-15 Acid etching modifies the surface of titanium to create a nano-scale (micron-level) alteration. Compared with PEEK and smooth titanium, acid-etched titanium stimulates a better osteogenic environment.^16,17 As this technology is now used clinically in spinal surgery, we thought it important to revisit the issue of CT analysis for fusion assessment with the newer titanium implants.

Artifact

The results of our study support the idea that the design of a titanium interbody fusion implant is important to radiographic analysis. The implant studied has a large open central aperture that appears to generate less artifact than historical controls (paired cylindrical cages) have.^1-4 Other investigators have reported fewer problems with artifact in their studies of implants incorporating larger openings for bone graft.^6,18 The radiologists in the present study found no significant problems with artifact. Less artifact is clinically important, as the remaining fusion variables can be more clearly visualized (Table 2, Figure 2).

Anterior Osseous Bridging, Subsidence, Lysis

In this study, the bony endplates were preserved. The disc and endplate cartilage was removed without reaming or drilling. Endplate reaming most likely contributes to subsidence and loss of original fixation between implant and bone interface.^1,4,12 Some authors have advocated recessing the cages deeply and then packing bone anteriorly to create a “sentinel fusion sign.”^1,2,6 Deeply seating interbody implants, instead of resting them more widely on the apophyseal ring of the vertebral endplate, may also lead to subsidence.^4,12 The issue of identifying a sentinel fusion sign is relevant only if the surgeon tries to create one. In the present study, the implant used was an impacted cage positioned on the apophyseal perimeter of the disc space, just slightly recessed, so there was no attempt to create a sentinel fusion sign, as reflected in the relatively low scores on anterior osseous bridging (48%, 52%).

Subsidence and peri-implant lysis are pathologic variables associated with motion and bone loss. Sethi and colleagues¹⁹ noted a high percentage of endplate resorption and subsidence in cases reviewed using PEEK or allograft spacers paired with BMP-2. Although BMP-2 was used in the present study, we found very low rates of subsidence (0%, 5%) and no significant peri-implant lucencies (2%, 4%) (Figure 2). Interobserver agreement for these variables was high (0.95, 0.96). We hypothesize that the combination of endplate-sparing surgical technique and implant–bone integration contributed to these results.

Trabecular Bone and Fusion Grade

The primary radiographic criterion for solid interbody fusion is trabecular bone throughout the cage, bridging the vertebral bodies. In our study, the success rates for this variable were 96% and 100%, and there was very high interobserver agreement (0.96) (Figure 3). This very high fusion rate may preclude detecting subtle differences in interobserver agreement, but to what degree, if any, is unknown. Other investigators have effectively identified trabecular bone across the interspace and throughout the cages.^6,18 The openings for bone formation were larger in the implants they used than in first-generation fusion cages but not as large as the implant openings in the present study. Larger openings may correlate with improved ability to visualize bridging bone on CT.

Radiologists and surgeons must ultimately arrive at a conclusion regarding the likelihood a fusion has occurred. Our radiologists integrated all the separate radiologic variables cited here, as well as their overall impressions of the scans, to arrive at a final grade regarding fusion quality (Figures 3, 4). Although this category provides the most interpretive latitude of all the variables examined, the results demonstrate high interobserver reliability. Agreement to exactly the same fusion grade was 0.77, and agreement to within 1 category grade was 0.95.

This study had several limitations. Surgical explorations were not clinically indicated and were not performed. There were no suspected nonunions or hardware complications, two of the most common indications for exploration. In addition, this study was conducted not to determine specific accuracy of CT (compared with surgery exploration) for fusion assessment but to assess interobserver reliability. The clinical success rates for this population were high, and no patient required revision surgery for suspected pseudarthrosis. To assess the true accuracy of CT for fusion assessment, one would have to subject patients to follow-up exploratory surgery to test fusions mechanically.

Another limitation is the lack of a single industry-accepted radiographic fusion grading system. Fusion criteria are not standardized across all studies. Our radiologists have extensive research experience and limit their practices to neuromuscular radiology with a concentration on the spine. The radiographic criteria cited here are the same criteria they use in clinical practice, when reviewing CT scans for clinicians. Last, there was no control group for direct comparison against other cages. Historical controls were cited. This does not adversely affect the conclusions of this investigation.

Conclusion

Clinicians have been reluctant to rely on CT with titanium devices because of concerns about the accuracy of image interpretations. The interbody device used in this study demonstrated minimal artifact and minimal subsidence, and trabecular bone was easily identified throughout the implant in the majority of cases reviewed. We found high interobserver agreement scores across all fusion criteria. Although surgical exploration remains the gold standard for fusion assessment, surgeons should have confidence in using CT with this titanium implant.