Unusual formation of the musculocutaneous and median nerves: a case report refined by intraneural dissection and literature review.

This report presents a detailed anatomical investigation of an upper limb specimen showing an atypical formation of the musculocutaneous nerve (MCN) and median nerve (MN). The study was refined by intraneural dissection, which supplements earlier descriptions of similar anatomical variations and allows for revision of the accepted classification. The case described in this report was an incidental finding during routine dissection of a fixed isolated upper limb. Intraneural dissection revealed partial fusion between the MCN and aberrant bundles of the MN. Those aberrant bundles joined the main steam of the MN at the level at which the MCN branched off as an independent nerve. The procedure allowed the aberrant fibres of the MN to be differentiated from the MCN. The presence of separate bundles in a territory corresponding to the MCN was confirmed, although those bundles and the aberrant MN bundles were covered by a common epineurium. The aberrant MN bundles running within the MCN did not contribute to innervation of the forearm muscles. They rejoined the main nerve trunk in the arm. A comprehensive understanding of the diverse anatomical variations of the upper limb nerves could be crucial for the safety and success of surgical procedures, especially procedures for reconstructing the brachial plexus or its branches.