Bilateral Presence of Axillary Arch Muscle Passing Through the Posterior Cord of the Brachial Plexus

The axillary arch can be described as an anomalous muscular slip of latissimus dorsi muscle. In this paper, a rare case of bilateral axillary arch is reported during routine dissection of the axillary region of a 57-year old male cadaver. On both sides, the axillary arch muscle took origin from latissimus dorsi and teres major, and passed upwards through the posterior cord of the brachial plexus, but posterior to the bulk of axillary neurovascular bundle. It then split into two slips: the medial slip was inserted into the root of the coracoid process, while the lateral slip which was intracapsular, was attached to the lesser tubercle, above the attachment of subscapularis. The presence of the muscle has important clinical implications, and the position, bilateral presence, penetration of the posterior cord, and multiple connective tissue attachments makes the case most unique. The anatomy, surgical implications, and embryology of the anomalous muscle are discussed in this paper.