A Cadaveric Case Report of a Brachial Myofascial Tunnel: A Rare Anatomical Variation and a Potential Site of Median Nerve and Brachial Artery Compression

Median nerve entrapment most commonly occurs at the wrist, though proximal compression due to rare fascial or myofascial variations is likely underrecognized. Fascial tunnels may persist during development or result from incomplete remodeling, creating confined spaces that predispose neurovascular structures to compression. Concurrent entrapment of both neural and vascular structures within the arm is particularly uncommon and may produce overlapping neuropathic and ischemic symptoms. We report a rare brachial myofascial tunnel identified at the junction of the middle and distal thirds of the arm. The tunnel enclosed both the median nerve and brachial artery over a 9.5 cm course extending to the cubital fossa. It possessed a thick fascial roof attached medially to the brachialis muscle and laterally to the medial intermuscular septum. Within the tunnel, the median nerve remained medial to the brachial artery, received a communicating branch from the musculocutaneous nerve, and demonstrated adhesions to the brachial artery and adjacent musculature, suggesting potential compressive interaction. Distally, the tunnel continued as a thin fascial band surrounding only the median nerve, while the brachial artery resumed its typical course. This prolonged shared neurovascular course within a confined tunnel represents a potential site of dual entrapment, with possible manifestations including proximal median neuropathy, exertional arm pain, or distal ischemic symptoms. Recognition of such anatomical variations is important for surgeons, anatomists, and clinicians, as unrecognized configurations may contribute to diagnostic uncertainty and increase the risk of iatrogenic injury during upper extremity procedures.