Resident Physician, PGY-3 New York-Presbyterian at Columbia/Cornell New York, New York, United States
Case Diagnosis: Neuropathy Secondary to Femoral Nerve Sheath Tumor
Case Description: A 26-year-old male with no history presented with lower extremity numbness and tingling. His symptoms began 1-month prior. He incidentally also noted a small soft tissue mass in his right inner thigh presumed to be a lipoma. He was diagnosed by an outside clinic with lumbar radiculopathy and prescribed PT. Two-weeks later, he went for further evaluation as he was not responding to PT. He described 2/10, tingling pain along his anteromedial leg and ankle that worsened with palpation of thigh lump and improved with walking. He denied back pain. Strength, sensation, gait, and lumbar component (special testing) of physical exam were within normal limits. Notably, right patellar reflex was absent. Inspection revealed a 2.5 by 5.0 cm thigh mass, and palpation reproduced his symptoms. Diagnostic ultrasound illustrated a large, hypoechoic, well-circumscribed structure deep to the adductor muscles and adjacent to the femoral artery.
Discussion: MRI of the right thigh was obtained, confirming the diagnosis of a femoral nerve sheath tumor. Peripheral nerve sheath tumors (PNST) are abnormal growths of myelin. The primary treatment is surgical excision, which he had with clean margins that significantly improved symptoms. However, he returned 5-months later with symptoms; ultrasound confirmed a recurrent femoral nerve sheath tumor. Sonographically, PNSTs have been described as hypoechoic, homogeneous structures with posterior acoustic shadowing, consistent with his sonographic images. MRI is used to confirm the diagnosis.
Conclusions: This case illustrates the importance of bedside ultrasound as a diagnostic tool for neuromusculoskeletal complaints. PNSTs can easily be misdiagnosed as lipomas. Through ultrasound evaluation, as well as an understanding of neuromuscular anatomy, this patient’s PNST was correctly diagnosed and appropriately treated. Furthermore, this case highlights the difficulty in treating PNSTs. While surgical excision remains the first line treatment, careful monitoring is required as PNSTs may recur.