Variant of the coracobrachialis muscle with a tunnel for the median nerve and brachial artery

This case report documents a variation in the insertion of the coracobrachialis muscle of the right arm of an adult male cadaver of unknown age. In addition to the normal insertion of the coracobrachialis muscle into the middle of the medial border of the humerus, an additional slender tendon passed inferiorly, crossing anterior to the median nerve and brachial artery before attaching to the medial epicondyle of the humerus. Most of the proximal part of the tendon gave rise to an aponeurotic expansion that inserted into the distal medial border of the humerus. The tendinous insertion and aponeurotic expansion may represent a variant of the coracobrachialis longus (Wood's) muscle and the internal brachial ligament, respectively. The median nerve and brachial artery traversed a tunnel bounded by the additional tendon and aponeurotic expansion as well as the usual humeral insertion of the coracobrachialis muscle. The clinical implication of this variation is that it may be a cause of median nerve entrapment and brachial artery compression.