An unusual case of accessory head of coracobrachialis muscle involving lateral cord of brachial plexus and its clinical significance.

Knowledge of anatomical variations in the peripheral nervous system is key in the interpretation of unusual clinical signs or during physical or diagnostic imaging. This case study is a description of an anatomical variation between the coracobrachialis muscle and brachial plexus. In a routine dissection in the human anatomy laboratory, we were faced with an anatomical variation in the coracobrachialis muscle, observed in the upper right limb of a male cadaver. The coracobrachialis muscle had a common origin at the apex of the coracoid process and then divided into two heads. The lateral head followed its normal course until insertion into the middle third of the humerus, while the medial head involved the lateral cord of the brachial plexus before insertion into the intermuscular septum in the proximal third of the humerus. Atypical anatomical variations have clinical and surgical implications in procedures such as brachial plexus block and lateral cord compression. In these cases the result could be paralysis of the flexor musculature of the forearm and hypoesthesia of the forearm.