Unusual bilateral variation in the origin, number and distribution pattern of pectoral nerves

During the dissection of a 69-year-old male cadaver, three pectoral nerves from the trunks and divisions of the brachial plexus were detected bilaterally. Superior pectoral nerves arose from the anterior divisions of the superior trunks. The middle pectoral nerve originated from the middle trunk on the right side and from the anterior division of the middle trunk on the left side and inferior pectoral nerves branched from the inferior trunks. What is peculiar in this case is the bi-laterality and the division of the middle pectoral nerves into anterior and posterior branches, where the posterior branches joined the inferior pectoral nerves to form a short common stem that innervated both pectoralis muscles.

Such variations could predispose the nerves to unintentional but preventable injuries during surgical, anesthesiologic and other clinical procedures, hence, clinicians should be aware of such variations of pectoral nerves to avoid technical errors, unintended injuries and treatment failures.