Ulnar neuropathy at the elbow is a common entrapment neuropathy, typically caused by mechanical compression within the cubital tunnel. Less commonly, space-occupying lesions such as lipomas may contribute, but are rarely reported in the literature and may be difficult to detect on standard imaging. Electrodiagnostic testing aids localization of focal lesions when imaging is inconclusive. A 19-year-old left-hand-dominant female presented with a 1-2 year history of progressive left medial elbow pain and paresthesias radiating to the fourth and fifth digits, worsened by elbow flexion and pressure. Physical exam revealed decreased sensation in the ulnar distribution, positive Tinel’s sign, full strength, and no atrophy. There was a painful, palpable subcutaneous mass distal to the cubital tunnel, with differential including ganglion cyst, lipoma, or other soft tissue mass. MRI demonstrated nonspecific soft tissue edema without a discrete mass. Electrodiagnostic testing showed a left ulnar motor neuropathy with normal conduction velocities but focal slowing on ulnar inching studies between 4-6 cm distal to the elbow, localizing the lesion. Given her persistent symptoms, palpable mass, and electrodiagnostic findings despite nondiagnostic imaging, a compressive etiology was supported. The patient underwent ulnar nerve transposition and mass excision. Pathology revealed a benign angiolipoma. At four months postoperatively, she had resolution of pain and paresthesias with full return to activities and no distal neurologic deficits aside from mild surgical site numbness. Long-term outcomes remain to be evaluated, though prognosis is favorable after excision with low risk of recurrence. This case highlights a rare cause of ulnar neuropathy due to angiolipoma, an uncommon lipoma subtype infrequently reported in the literature, especially at the elbow. While MRI typically identifies soft tissue masses, small or poorly defined lesions like angiolipomas may be missed. Thus, electrodiagnostic testing, combined with clinical findings, is critical for lesion localization and management when imaging is nondiagnostic.
