Removal of a giant musculocutaneous nerve schwannoma under intraoperative neurophysiological monitoring: Case report video and review of the literature.

Schwannomas of the musculocutaneous nerve (MCN) are rare benign tumors of the peripheral nerve sheath. Due to their slow growth, they are often diagnosed late. In the upper limbs, schwannomas typically affect longer peripheral nerves at a distal level, making MCN cases uncommon. Ultrasound (US) and magnetic resonance imaging (MRI) are essential tools for early detection. While most schwannomas can be surgically removed without damaging the nerve, intraoperative neurophysiological monitoring (IONM) is critical if fascicular involvement exists. We present a 73-year-old right-handed Jehovah's Witness with a history of mild polio affecting the right arm. MRI showed a slow-growing, cystic mass in the right biceps, originating from the MCN and suggestive of schwannoma. Surgery achieved gross total resection without nerve damage. Histopathology confirmed a cystic schwannoma. In atypical proximal upper limb tumors, MCN schwannoma should be considered, with US/MRI crucial for diagnosis. IONM-assisted removal can minimize postoperative complications.