- Email: [email protected]
Intraneural Lipoma of the Tibial Nerve: A Case Report
The Journal of Foot & Ankle Surgery xxx (2016) 1–4
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Case Reports and Series
Intraneural Lipoma of the Tibial Nerve: A Case Report Tarin B. Krzywosinski, DPM 1, Adam L. Bingham, DPM 2, Lawrence M. Fallat, DPM, FACFAS 3 1
Second Year Surgical Resident, Department of Podiatric Surgery, Beaumont Hospital-Wayne, Wayne, MI Foot and Ankle Surgeon, Foot and Ankle Specialty Clinic, Russellville, AR 3 Director, Podiatric Surgical Residency, Beaumont Hospital-Wayne, Wayne, MI 2
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
Intraneural lipomas, neurofibrolipomas, lipofibromatous hamartomas, and perineural lipomas are subsets of hamartomas that typically present as fibroadipose, soft tissue masses within the epineurium of a nerve. Several cases involving intraneural lipomas of the median nerve in the upper extremity have been reported; however, owing to the lesion’s rare incidence in the foot and ankle, only a select few cases involving the superficial peroneal nerve have been reported. We present the first case of a tibial nerve intraneural lipoma in a 42-year-old female with a follow-up period of 2 years. We discuss the clinical presentation, distinguishing features, surgical procedures, and short-term outcome regarding this unique tumor. Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: lipofibromatous hamartoma neural fibrolipoma neurolipomatosis perineural lipoma
Intraneural lipomas (INLs) are benign soft tissue masses composed of mature fat cells that present as firm, glistening, pink-yellow tumors most commonly found in the median nerve of the upper extremity (1). Occasionally, this condition is associated with variations of macrodactyly and bony proliferation known as macrodystrophia lipomatosa or proteus syndrome (2–4). Clinically, these soft tissue masses can be painful or painless and have a tendency to arise in areas of the body prone to nerve impingement, such as the wrist, elbow, and ankle. The common symptoms associated with INLs are altered sensation or motor function along the distribution of the affected nerve, a positive Tinel’s sign, and pain, likely due to compression of the nerve fibers by a fibrofatty infiltrate in a confined space (5–7). Nerve conduction velocities can also be reduced, and a pathognomonic finding is a serpiginous “cable-like” appearance on magnetic resonance imaging (MRI) (5). Because of the limited number of foot and ankle INLs discussed in published studies, definitive treatment options and guidelines have yet to be determined for this lesion. Conservative treatment options involve monitoring the size of the lesion and associated sensorymotor deficits. Surgical treatment options include debulking of the mass, resection of the mass, or en bloc resection of the nerve. Also, owing to the benign nature of the lesion, investigators believe recurrence of the mass is unlikely after adequate resection (8). Some investigators have recommended abstaining from surgical excision of
Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Tarin Krzywosinski, DPM, Beaumont Hospital Wayne, 33155 Annapolis Road, Wayne, MI 48184. E-mail address: [email protected] (T.B. Krzywosinski).
asymptomatic masses, unless the INL is a cosmetic concern for the patient (6,7). Case Report The patient was a 42-year-old nondiabetic female who presented to our outpatient clinic in February 2014 with a progressively painful and slow-growing soft tissue mass along the medial aspect of her right ankle. The mass was present for an unknown period but had become symptomatic during the course of 1 year. On initial examination, the mass was firm and slightly mobile, with no transillumination. She experienced pain on palpation, with a positive Tinel’s sign with percussion of the tibial nerve. No sensory deficits were noted with a Semmes-Weinstein 5.07-g monofilament wire. No abnormalities were detected in the nerve conduction velocity or electromyogram studies. No gross muscular deficits such as atrophy or weakness were noted in the lower extremity. The findings from plain films were also negative; thus, to further assess the mass, a MRI scan was ordered. The T1-weighted images showed a 3-cm 2-cm 10-cm hyperintense, internally striated, bilobed mass adjacent to the tarsal tunnel and extending to the knot of Henry (Figs. 1 and 2). The striations were consistent with the pathognomonic “cable-like” appearance of INLs on MRI; however, owing to the increased signal intensity at the distal aspect of the mass on the T2-weighted images, liposarcoma could not be ruled out (Figs. 3 and 4). After discussing the conservative treatment options and because of the rapid growth and painful nature of the lesion, we recommended surgical excision of the mass. The goals of surgery involved identification and excision of the mass and decompression of the tibial nerve. The patient was brought to the operating room and placed on the
1067-2516/$ - see front matter Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2016.07.002
2
T.B. Krzywosinski et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–4
Fig. 1. Magnetic resonance T1-weighted image, plantar view, showing the hyperintense, internally striated, bilobed mass adjacent to the tarsal tunnel.
Fig. 3. Pathognomonic “cable-like” appearance of intraneural lipomas on magnetic resonance imaging.
operating room table in a supine position. A thigh tourniquet was applied to the extremity and inflated to 325 mm Hg. Intraoperatively, it was noted that the mass extended to the bifurcation of the tibial nerve; thus, dissection through the flexor retinaculum, porta pedis, and medial and lateral plantar tunnels was necessary to completely expose the INL (Fig. 5). Once exposed, the mass appeared to be encapsulated within the epineurium of the tibial nerve and was not attached to any surrounding vascular structures. Furthermore, a few small, clinically insignificant nerve fibers that were well-adhered to the capsule of the mass were deemed unsalvageable and were resected with the mass using a bipolar coagulator. Owing to the size of the mass and its unknown origin, dissection was performed without the use of loupe magnification. The mass was successfully excised, with preservation of most of the tibial nerve and all nearby vascular structures (Figs. 6 and 7). The specimen was tagged proximally and distally for pathologic evaluation, which revealed mature adipose tissue with interspersed fibrous tissue (Figs. 8 and 9). No nerve fascicles were noted within the mass. A drain was placed in the dead space, the flexor retinaculum was repaired, and closure was
completed in layers. The incision site was dressed with saline-soaked Owen’s silk and covered with a sterile compressive dressing consisting of 4 4 gauze and a gauze roll. Postoperatively, the patient’s surgical incision dehisced at the proximal and distal aspect but was successfully addressed with local wound care consisting of serial debridement, gradient compression dressings, and application of collagenase or antibiotic ointment (Fig. 10). At the 6-month follow-up point, the patient reported experiencing mild sensory deficits along the course of the proper branch of the medial plantar nerve, but no motor deficits were noted at any time throughout the postoperative course. At the 2-year follow-up period, the patient related minimal pain, minor residual sensory deficits, and no difficulty in performing her daily tasks at work or home.
Fig. 2. Magnetic resonance T1-weighted image, lateral view, showing the hyperintense, internally striated, bilobed mass adjacent to the tarsal tunnel.
Fig. 4. T2-weighted magnetic resonance image showing increased signal intensity in the distal mass, possibly indicative of a liposarcoma.
Discussion The purpose of this case report was to present a rare INL involving the tibial nerve of the lower extremity. To the best of our
T.B. Krzywosinski et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–4
3
Fig. 5. Intraoperative dissection of the soft tissue mass extending to the bifurcation of the tibial nerve.
Fig. 7. Further excision of the mass with preservation of the tibial nerve.
knowledge, this is the first reported case involving the tibial nerve. Other reports discussing lower extremity INLs have included the superficial peroneal nerve or medial plantar nerve involvement (8). Some investigators have differentiated between encapsulated versus infiltrative INLs. The encapsulated form has been reported to occur in the fourth to fifth decade of life and can be easily excised, with trivial injury to the surrounding nerves. In contrast, infiltrative INLs consist of longitudinal fatty streaks that surround and separate nonhypertrophied nerve fascicles, making it difficult to excise without damaging the affected nerve (9). An MRI T1-weighted image might detect infiltration of fibroadipose tissue by revealing a hyperintense signal with hypointense septations, indicating that the nerve bundles are separated by fat (10). This gives the mass its pathognomonic serpiginous “cable-like” appearance on MRI (5). The mass in our patient appeared well-encapsulated and did contain septations; however, these septations were likely due to fibrous tissue rather than separated nerve fascicles. Microscopically, INLs can contain fibrofatty infiltrates, abundant collagen, or atrophic nerves with a thick perineurium. It is important to note the lack of mitotic figures, atypia, and other signs indicative of malignancy, which will differentiate the mass from a liposarcoma (11,12). Liposarcomas present with the same symptoms as INLs, have a strong predilection for the lower extremity, and are the second most common soft tissue sarcoma in adults (12). Liposarcomas are a must-not-miss lesion owing to their high degree of malignancy. The differential diagnosis should also include neuroma, ganglion cyst, lipoma, vascular malformation linked with Klippel-Trenaunay syndrome, and neurilemmoma (5,6). The etiology of INLs is unknown; however, the soft tissue masses tend to arise in areas of impingement such as the wrist and elbow.
One theory discussed by Bibbo and Warren (12) and later by Al-Jabri et al (5) involves impingement on the nerve by a retinaculum or ligament that thus causes chronic repetitive microtrauma. Impingement of the tibial nerve in the tarsal tunnel could have caused the formation of our patient’s INL; however, a direct correlation or causation could not be determined. It is possible that the limited amount of space in the tarsal tunnel, combined with the mass effect of the lesion, compressed the nerve, causing pain. Additionally, Sabapathy et al (7) discussed a theory involving benign proliferation of the fatty outer epineurial nerve sheath, and Akisue et al (11) investigated the proliferation of endoneurial tissue caused by deposition of CD34 antigen– antibody complexes with the S-100 protein. Although nerve conduction velocity studies and MRI findings can assist with the diagnosis and surgical planning, they are not essential. It would be reasonable to proceed with surgical excision without these diagnostic studies. Clinical examination findings such as muscle weakness or atrophy in the distribution of the affected nerve can indicate a nervous origin of the mass; however, our patient did not exhibit any of these signs. For well-encapsulated lesions, the treatment of choice is complete resection of the mass, and loupe magnification to assist with dissection should be considered when operating on a peripheral nerve tumor. In 2005, Jung et al (13) completely resected symmetrical digital INLs in the hands without residual sensory deficits or recurrence during a follow-up period of 15 months. For infiltrative lesions, the physician might consider debulking a portion of the space-occupying lesion or complete en bloc resection of a purely sensory nerve, including burial of the proximal stump. Neurosurgeons typically will not recommend intrafascicular debulking of infiltrative INLs, because the procedure initiates a vicious circle of fibrosis and ischemia (14). Fransen et al (15) discussed
Fig. 6. Excision of the mass, with preservation of the tibial nerve.
Fig. 8. Gross specimen tagged proximally and distally for pathologic evaluation.
4
T.B. Krzywosinski et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–4
Fig. 9. Hematoxylin and eosin-stained slide of the specimen containing mature adipose tissue with interspersed fibrous tissue at low magnification (40). No nerve fascicles were noted within the mass.
Fig. 10. Healed surgical site after local wound care.
References amputation as a viable treatment option of a lesion associated with macrodactyly involving the second ray of the foot; however, owing to the location of the lesion in our patient, this was not a practical treatment option. Additional postoperative complications discussed in published studies include sensory and motor deficits, axonal injury, and myelin sheath degeneration. Both Ogose et al (16) and Mam et al (17) sacrificed the sensory nerves during en bloc resection in their case studies, and all patients experienced postoperative sensory deficits. Our patient’s lesion was well-encapsulated; thus, en bloc resection of the INL using a bipolar coagulator was performed, with preservation of the tibial nerve. Before visualizing the lesion intraoperatively, our team was unable to confirm the tumor was of nervous origin; however, we believe that during peripheral nerve surgery, the surgical team should be prepared to perform nerve reconstruction in the case of a residual nerve defect after mass excision. The few postoperative complications our patient experienced were localized residual numbness, confirmed with the Semmes-Weinstein 5.07-g monofilament test on the plantar medial arch at the 2-year followup visit and wound dehiscence after surgery. Both were trivial to our patient’s overall satisfaction. In conclusion, our case presentation justifies complete resection of the mass as a reasonable treatment option for symptomatic INLs because the procedure alleviated our patient’s pain with minor postoperative complications. In general, the incidence of INLs in the lower extremity is very low, and the few reported cases have involved the superficial peroneal nerve. We have presented the first case involving the tibial nerve, with discussion regarding the clinical presentation, distinguishing features, surgical procedures, and shortterm outcomes of lower extremity INLs.
1. Silverman TA, Enzinger FM. Fibrolipomatous hamartoma of nerve. Am J Surg Pathol 9:7–14, 1985. 2. Taddie KL, Fallat LM. Lipofibromatous hamartoma of nerve. J Foot Ankle Surg 46:116–119, 2007. 3. Enzinger F, Weiss D. Fibrohystiocytic Tumors of Intermediate Malignancy. Soft Tissue Tumors, ed 3, Mosby, St. Louis, 1994, p. 332. 4. Bailey E, Thompson F. Macrodystrophia lipomatosa of the foot: a report of three cases and literature review. Foot Ankle Int 18:89–93, 1997. 5. Al-Jabri T, Garg S, Mani GV. Lipofibromatous hamartoma of the median nerve. J Orthop Surg Res 5:71, 2010. 6. Donley BG, Neel M, Mitias HM. Neural fibrolipoma of the foot: a case report. Foot Ankle Int 17:712–713, 1996. 7. Sabapathy SR, Langer V, Bhatnagar A. Intraneural lipoma associated with a branch of the superficial peroneal nerve. J Foot Ankle Surg 47:576–578, 2008. 8. Amadio P, Relman H, Dobyns J. Lipofibromatous hamartoma of nerve. J Hand Surg 13:67–75, 1988. 9. Balakrishnan C, Bachusz R, Balakrishnan A, Elliot D, Carega D. Intraneural lipoma of the radial nerve presenting with Wartenberg syndrome: a case report and review of literature. Can J Plast Surg 17:e39–e41, 2009. 10. DecMaeseneer M, Jaovisidha S, Lenchik L, Witte D, Schweitzer ME, Sartoris DJ, Resnick D. Fibrolipomatous hamartoma: MR imaging findings. Skeletal Radiol 26:155–160, 1997. 11. Akisue T, Matsumoto K, Yamamoto T, Kizaki T, Fujita I, Yoshiya S, Kurosaka M. Neural fibrolipoma of the superficial peroneal nerve in the ankle: a case report with immunohistochemical analysis. Pathol Int 52:730–733, 2002. 12. Bibbo C, Warren AM. Fibrolipomatous hamartoma of nerve. J Foot Ankle Surg 33:64–71, 1994. 13. Jung SN, Yim Y, Kwon H, Yonsei Med J. Symmetric lipofibromatous hamartoma of affecting digital nerves. Yonsei Med J 46:169–172, 2005. 14. Mohanty CB, Midha R. Lipomatosis of nerve. World Neurosurg 82:331–332, 2014. 15. Fransen BL, Broeders MG, van Oosterom FJ, Gilhuijs ND, Burger BJ. Operative resection is a viable treatment of macrodactyly of the foot caused by lipofibromatous hamartoma: a case study with a 5 year follow up. Foot Ankle Surg 20:47–50, 2014. 16. Ogose A, Hotta T, Higuchi T, Katsumi N, Koda H, Umezu H. Fibrolipomatous hamartoma in the foot: magnetic resonance imaging and surgical treatment a report of two cases. J Bone Joint Surg Am 84:432–436, 2002. 17. Mam P, Lewis EB, Song T, Bakotic BW. Fibrolipomatous hamartoma of nerve in the great toe. J Am Podiatr Med Assoc 104:531–534, 2014.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Case Reports and Series
Intraneural Lipoma of the Tibial Nerve: A Case Report Tarin B. Krzywosinski, DPM 1, Adam L. Bingham, DPM 2, Lawrence M. Fallat, DPM, FACFAS 3 1
Second Year Surgical Resident, Department of Podiatric Surgery, Beaumont Hospital-Wayne, Wayne, MI Foot and Ankle Surgeon, Foot and Ankle Specialty Clinic, Russellville, AR 3 Director, Podiatric Surgical Residency, Beaumont Hospital-Wayne, Wayne, MI 2
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
Intraneural lipomas, neurofibrolipomas, lipofibromatous hamartomas, and perineural lipomas are subsets of hamartomas that typically present as fibroadipose, soft tissue masses within the epineurium of a nerve. Several cases involving intraneural lipomas of the median nerve in the upper extremity have been reported; however, owing to the lesion’s rare incidence in the foot and ankle, only a select few cases involving the superficial peroneal nerve have been reported. We present the first case of a tibial nerve intraneural lipoma in a 42-year-old female with a follow-up period of 2 years. We discuss the clinical presentation, distinguishing features, surgical procedures, and short-term outcome regarding this unique tumor. Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: lipofibromatous hamartoma neural fibrolipoma neurolipomatosis perineural lipoma
Intraneural lipomas (INLs) are benign soft tissue masses composed of mature fat cells that present as firm, glistening, pink-yellow tumors most commonly found in the median nerve of the upper extremity (1). Occasionally, this condition is associated with variations of macrodactyly and bony proliferation known as macrodystrophia lipomatosa or proteus syndrome (2–4). Clinically, these soft tissue masses can be painful or painless and have a tendency to arise in areas of the body prone to nerve impingement, such as the wrist, elbow, and ankle. The common symptoms associated with INLs are altered sensation or motor function along the distribution of the affected nerve, a positive Tinel’s sign, and pain, likely due to compression of the nerve fibers by a fibrofatty infiltrate in a confined space (5–7). Nerve conduction velocities can also be reduced, and a pathognomonic finding is a serpiginous “cable-like” appearance on magnetic resonance imaging (MRI) (5). Because of the limited number of foot and ankle INLs discussed in published studies, definitive treatment options and guidelines have yet to be determined for this lesion. Conservative treatment options involve monitoring the size of the lesion and associated sensorymotor deficits. Surgical treatment options include debulking of the mass, resection of the mass, or en bloc resection of the nerve. Also, owing to the benign nature of the lesion, investigators believe recurrence of the mass is unlikely after adequate resection (8). Some investigators have recommended abstaining from surgical excision of
Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Tarin Krzywosinski, DPM, Beaumont Hospital Wayne, 33155 Annapolis Road, Wayne, MI 48184. E-mail address: [email protected] (T.B. Krzywosinski).
asymptomatic masses, unless the INL is a cosmetic concern for the patient (6,7). Case Report The patient was a 42-year-old nondiabetic female who presented to our outpatient clinic in February 2014 with a progressively painful and slow-growing soft tissue mass along the medial aspect of her right ankle. The mass was present for an unknown period but had become symptomatic during the course of 1 year. On initial examination, the mass was firm and slightly mobile, with no transillumination. She experienced pain on palpation, with a positive Tinel’s sign with percussion of the tibial nerve. No sensory deficits were noted with a Semmes-Weinstein 5.07-g monofilament wire. No abnormalities were detected in the nerve conduction velocity or electromyogram studies. No gross muscular deficits such as atrophy or weakness were noted in the lower extremity. The findings from plain films were also negative; thus, to further assess the mass, a MRI scan was ordered. The T1-weighted images showed a 3-cm 2-cm 10-cm hyperintense, internally striated, bilobed mass adjacent to the tarsal tunnel and extending to the knot of Henry (Figs. 1 and 2). The striations were consistent with the pathognomonic “cable-like” appearance of INLs on MRI; however, owing to the increased signal intensity at the distal aspect of the mass on the T2-weighted images, liposarcoma could not be ruled out (Figs. 3 and 4). After discussing the conservative treatment options and because of the rapid growth and painful nature of the lesion, we recommended surgical excision of the mass. The goals of surgery involved identification and excision of the mass and decompression of the tibial nerve. The patient was brought to the operating room and placed on the
1067-2516/$ - see front matter Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2016.07.002
2
T.B. Krzywosinski et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–4
Fig. 1. Magnetic resonance T1-weighted image, plantar view, showing the hyperintense, internally striated, bilobed mass adjacent to the tarsal tunnel.
Fig. 3. Pathognomonic “cable-like” appearance of intraneural lipomas on magnetic resonance imaging.
operating room table in a supine position. A thigh tourniquet was applied to the extremity and inflated to 325 mm Hg. Intraoperatively, it was noted that the mass extended to the bifurcation of the tibial nerve; thus, dissection through the flexor retinaculum, porta pedis, and medial and lateral plantar tunnels was necessary to completely expose the INL (Fig. 5). Once exposed, the mass appeared to be encapsulated within the epineurium of the tibial nerve and was not attached to any surrounding vascular structures. Furthermore, a few small, clinically insignificant nerve fibers that were well-adhered to the capsule of the mass were deemed unsalvageable and were resected with the mass using a bipolar coagulator. Owing to the size of the mass and its unknown origin, dissection was performed without the use of loupe magnification. The mass was successfully excised, with preservation of most of the tibial nerve and all nearby vascular structures (Figs. 6 and 7). The specimen was tagged proximally and distally for pathologic evaluation, which revealed mature adipose tissue with interspersed fibrous tissue (Figs. 8 and 9). No nerve fascicles were noted within the mass. A drain was placed in the dead space, the flexor retinaculum was repaired, and closure was
completed in layers. The incision site was dressed with saline-soaked Owen’s silk and covered with a sterile compressive dressing consisting of 4 4 gauze and a gauze roll. Postoperatively, the patient’s surgical incision dehisced at the proximal and distal aspect but was successfully addressed with local wound care consisting of serial debridement, gradient compression dressings, and application of collagenase or antibiotic ointment (Fig. 10). At the 6-month follow-up point, the patient reported experiencing mild sensory deficits along the course of the proper branch of the medial plantar nerve, but no motor deficits were noted at any time throughout the postoperative course. At the 2-year follow-up period, the patient related minimal pain, minor residual sensory deficits, and no difficulty in performing her daily tasks at work or home.
Fig. 2. Magnetic resonance T1-weighted image, lateral view, showing the hyperintense, internally striated, bilobed mass adjacent to the tarsal tunnel.
Fig. 4. T2-weighted magnetic resonance image showing increased signal intensity in the distal mass, possibly indicative of a liposarcoma.
Discussion The purpose of this case report was to present a rare INL involving the tibial nerve of the lower extremity. To the best of our
T.B. Krzywosinski et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–4
3
Fig. 5. Intraoperative dissection of the soft tissue mass extending to the bifurcation of the tibial nerve.
Fig. 7. Further excision of the mass with preservation of the tibial nerve.
knowledge, this is the first reported case involving the tibial nerve. Other reports discussing lower extremity INLs have included the superficial peroneal nerve or medial plantar nerve involvement (8). Some investigators have differentiated between encapsulated versus infiltrative INLs. The encapsulated form has been reported to occur in the fourth to fifth decade of life and can be easily excised, with trivial injury to the surrounding nerves. In contrast, infiltrative INLs consist of longitudinal fatty streaks that surround and separate nonhypertrophied nerve fascicles, making it difficult to excise without damaging the affected nerve (9). An MRI T1-weighted image might detect infiltration of fibroadipose tissue by revealing a hyperintense signal with hypointense septations, indicating that the nerve bundles are separated by fat (10). This gives the mass its pathognomonic serpiginous “cable-like” appearance on MRI (5). The mass in our patient appeared well-encapsulated and did contain septations; however, these septations were likely due to fibrous tissue rather than separated nerve fascicles. Microscopically, INLs can contain fibrofatty infiltrates, abundant collagen, or atrophic nerves with a thick perineurium. It is important to note the lack of mitotic figures, atypia, and other signs indicative of malignancy, which will differentiate the mass from a liposarcoma (11,12). Liposarcomas present with the same symptoms as INLs, have a strong predilection for the lower extremity, and are the second most common soft tissue sarcoma in adults (12). Liposarcomas are a must-not-miss lesion owing to their high degree of malignancy. The differential diagnosis should also include neuroma, ganglion cyst, lipoma, vascular malformation linked with Klippel-Trenaunay syndrome, and neurilemmoma (5,6). The etiology of INLs is unknown; however, the soft tissue masses tend to arise in areas of impingement such as the wrist and elbow.
One theory discussed by Bibbo and Warren (12) and later by Al-Jabri et al (5) involves impingement on the nerve by a retinaculum or ligament that thus causes chronic repetitive microtrauma. Impingement of the tibial nerve in the tarsal tunnel could have caused the formation of our patient’s INL; however, a direct correlation or causation could not be determined. It is possible that the limited amount of space in the tarsal tunnel, combined with the mass effect of the lesion, compressed the nerve, causing pain. Additionally, Sabapathy et al (7) discussed a theory involving benign proliferation of the fatty outer epineurial nerve sheath, and Akisue et al (11) investigated the proliferation of endoneurial tissue caused by deposition of CD34 antigen– antibody complexes with the S-100 protein. Although nerve conduction velocity studies and MRI findings can assist with the diagnosis and surgical planning, they are not essential. It would be reasonable to proceed with surgical excision without these diagnostic studies. Clinical examination findings such as muscle weakness or atrophy in the distribution of the affected nerve can indicate a nervous origin of the mass; however, our patient did not exhibit any of these signs. For well-encapsulated lesions, the treatment of choice is complete resection of the mass, and loupe magnification to assist with dissection should be considered when operating on a peripheral nerve tumor. In 2005, Jung et al (13) completely resected symmetrical digital INLs in the hands without residual sensory deficits or recurrence during a follow-up period of 15 months. For infiltrative lesions, the physician might consider debulking a portion of the space-occupying lesion or complete en bloc resection of a purely sensory nerve, including burial of the proximal stump. Neurosurgeons typically will not recommend intrafascicular debulking of infiltrative INLs, because the procedure initiates a vicious circle of fibrosis and ischemia (14). Fransen et al (15) discussed
Fig. 6. Excision of the mass, with preservation of the tibial nerve.
Fig. 8. Gross specimen tagged proximally and distally for pathologic evaluation.
4
T.B. Krzywosinski et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–4
Fig. 9. Hematoxylin and eosin-stained slide of the specimen containing mature adipose tissue with interspersed fibrous tissue at low magnification (40). No nerve fascicles were noted within the mass.
Fig. 10. Healed surgical site after local wound care.
References amputation as a viable treatment option of a lesion associated with macrodactyly involving the second ray of the foot; however, owing to the location of the lesion in our patient, this was not a practical treatment option. Additional postoperative complications discussed in published studies include sensory and motor deficits, axonal injury, and myelin sheath degeneration. Both Ogose et al (16) and Mam et al (17) sacrificed the sensory nerves during en bloc resection in their case studies, and all patients experienced postoperative sensory deficits. Our patient’s lesion was well-encapsulated; thus, en bloc resection of the INL using a bipolar coagulator was performed, with preservation of the tibial nerve. Before visualizing the lesion intraoperatively, our team was unable to confirm the tumor was of nervous origin; however, we believe that during peripheral nerve surgery, the surgical team should be prepared to perform nerve reconstruction in the case of a residual nerve defect after mass excision. The few postoperative complications our patient experienced were localized residual numbness, confirmed with the Semmes-Weinstein 5.07-g monofilament test on the plantar medial arch at the 2-year followup visit and wound dehiscence after surgery. Both were trivial to our patient’s overall satisfaction. In conclusion, our case presentation justifies complete resection of the mass as a reasonable treatment option for symptomatic INLs because the procedure alleviated our patient’s pain with minor postoperative complications. In general, the incidence of INLs in the lower extremity is very low, and the few reported cases have involved the superficial peroneal nerve. We have presented the first case involving the tibial nerve, with discussion regarding the clinical presentation, distinguishing features, surgical procedures, and shortterm outcomes of lower extremity INLs.
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