Schwannoma Within a Muscular Nerve Branch to the Medial Head of Triceps: A Case Report.

Introduction and Importance: Schwannomas are rare, benign, encapsulated tumours arising within peripheral nerve sheath Schwann cells. Only 19% of schwannomas occur in the upper limb, typically affecting major peripheral nerves on the flexor aspect distal to the elbow. No reports have documented a schwannoma originating from a muscular branch to the medial head of the triceps brachii. This case highlights a unique anatomical presentation and the diagnostic challenges associated with atypical schwannomas. Presentation of Case: A 37-year-old female presented with a 4-year history of nonspecific neurological symptoms, including dysesthesia and swelling over the posteromedial aspect of her left arm. Initial investigations were inconclusive, but magnetic resonance imaging identified a tumour within the medial head of the triceps. Surgical excision revealed a well-encapsulated tumour within a muscular nerve branch to the medial head of the triceps. Histopathology confirmed a schwannoma. Postoperatively, the patient experienced complete symptom resolution with no complications at 3 months. Clinical Discussion: The unusual location of the schwannoma may have contributed to the diagnostic delay. Cadaveric studies suggest that innervation to the medial head of the triceps can have several anatomic variations, including innervation from the ulnar nerve, the nerve in which schwannomas are most commonly located. Conclusion: This case underscores the importance of considering peripheral nerve tumours in patients with persistent, unexplained upper limb symptoms. Awareness of atypical anatomical variants and careful imaging interpretation are essential for timely diagnosis and effective management.