A Prefixed Four-Trunk Brachial Plexus with Anomalous Anatomy of All Subsequent Divisions, Cords, and Terminal Branches: A Cadaveric Case Report.

BACKGROUND The brachial plexus is a complex neural structure providing motor and sensory innervation to structures of the arm, shoulder, and upper chest. The anatomical structure is typically divided into roots, trunks, divisions, and cords. Due to the presence of multiple nerve roots and branches, anatomical variations are common. Awareness of variations from normal anatomy is important in imaging, administration of nerve blocks, and surgical procedures of the neck and shoulder region. CASE REPORT We present a case of multiple anatomic variations of the right brachial plexus identified in a cadaver during routine dissection. To summarize, we identified a prefixed plexus with anomalous contributions from the C4 nerve root. Nerve roots C4 and C5 emerged anterior to the anterior scalene muscle. Furthermore, 4 trunks, rather than the typical 3, gave rise to multiple anomalies in the branching pattern of the distal divisions and cords. To the best of our knowledge, this is the first such case reported in the published literature. CONCLUSIONS The current case report presents a combination of brachial plexus anomalies not previously described in the medical literature - specifically, a prefixed (C4-T1) brachial plexus positioned anterior to the anterior scalene muscle with anomalies of the trunks, divisions, cords, and terminal branches. The variations presented have implications in neurogenic compression, interscalene blocks, and trauma to the upper limb. Knowledge of these anomalies may better equip anatomists and clinicians to understand pathology and intervention of the upper limb.