Median and musculocutaneous nerves: variant formation and distribution.

An unusual formation of the median and musculocutaneous nerves was observed during routine dissection of the left upper limb of a 60-year-old Caucasian male cadaver. The median nerve was formed by the fusion of three roots, two from the lateral and one from the medial cord of the brachial plexus. The variant lateral root of the median nerve followed an anomalous course, crossing anterior to the distal part of the axillary artery. Moreover, in the distal half of the arm, the median nerve contributed a communicating branch to the musculocutaneous nerve. Injury to such a variant median nerve in the proximal arm may lead to paresthesia along the preaxial border of the forearm, weakness of elbow flexion, in addition to other manifestations of median nerve injury. The developmental and clinical significance of this anomaly is discussed.