A rare bilateral variant of the coracobrachialis muscle with supernumerary heads and coexisted variant branching patterns of the brachial plexus and the axillary artery

Purpose The study report describes a rare bilateral variant of a six- and five-headed coracobrachialis muscle (CB). The musculocutaneous nerve (MCN) (bilaterally) and the median nerve (MN) lateral root (unilaterally) pierced CB heads, separating superficial from deep heads. Methods The variant bilateral CB was identified in a 78-year-old formalin-embalmed male cadaver, derived from a body donation program after a signed informed consent. Results At the right side: The 6-headed CB was pierced by the MCN, while the MN lateral root pierced the one superficial and deep head. CB was supplied by the lateral cord and the MCN. At the left side: A 5-headed CB was identified with three superficial distinct origins that fused into a common superficial head coursing anterior to MCN. The variant CB bilaterally (with 11 heads in total) coexisted with a MN variant formation, an atypical course of the MN lateral root through CB (right side), a connection of the MN lateral root with the MCN (left side) and a variant axillary artery branching pattern (bilaterally). Conclusions Course and direction of the accessory CB heads may occasionally entrap the MCN and/or adjacent structures (brachial artery and MN). The MCN compression results in problems in the glenohumeral joint flexion and adduction, and tingling or numbness of the elbow joint, the forearm lateral parts and the hand.