Brachial Plexus Abnormalities with Delayed Median Nerve Convergence: A Cadaveric Case Report

Introduction: The brachial plexus (BP) is a network of nerves responsible for the motor and sensory innervation of the upper limb. Complex pathology of this structure nerve may result in clinical consequences. We present a unique set of BP abnormalities involving the C4-C6 nerve roots, superior and middle trunks, additional communicating branches, and delayed median nerve union.

Methods: A routine dissection of a 70-year-old Caucasian female human body donor was performed. The neck, shoulder, and upper limb regions were intact prior to the dissection with no apparent deformities, surgical intervention, or significant trauma. The cadaver was dissected in a supine position. After removing the superficial fascia, the pectoralis muscles were reflected. The long head of the biceps brachii muscles was parted, revealing the brachial artery. This artery was traced back to the axillary artery. The plexus trunks, divisions, and terminal nerves were carefully teased from the surrounding connective tissue.

Results: The C4 root contributed to C5 before the superior trunk formed, resulting in a superior trunk composed of C4-C6. The C5 root was located anterior to the anterior scalene muscle, whereas C6 maintained its usual posterior position. Additionally, an anterior communicating branch from the middle trunk to the posterior cord was observed. A communicating branch between the lateral and medial cords split into two terminal branches: one merged with the ulnar nerve, and the other joined the medial contribution of the median nerve. The median nerve contributions from the lateral and medial cords merged approximately two inches above the elbow.

Conclusion : This rare combination of BP anomalies has not been previously described in the literature and are of significant clinical relevance. The additional anterior communicating branch from the middle trunk may suggest potential flexor muscle innervation by the posterior cord, which typically innervates extensor muscles. Additionally, delayed convergence of the median nerve may provide a protective mechanism in cases of midshaft humeral fracture. Awareness of these peripheral nerve abnormalities is important for diagnostic imaging, surgery, or peripheral nerve blocks.