A Variant Two Trunked Brachial Plexus with Complete Fusion of Musculocutaneous & Median Nerve – A Case Report

Brachial plexus is a network of spinal nerves supplying the upper limb with the root value C5-T1. These roots join with each other to form three trunks viz; the upper, middle and lower by union of C5, C6; continuation of C7 and union of the C8 and T1 respectively. During the routine dissection of left upper limb of an adult male cadaver, a variant pattern of two trunked brachial plexus was encountered. The upper trunk was formed by fusion of C5, C6 & C7 roots. The C7 root instead of continuing as middle trunk, joined with roots of C5 and C6 to form upper trunk. However formation of lower trunk was normal i.e. formed by union of C8 & T1. Additionally on this side, the musculocutaneous nerve was not piercing the coracobracialis muscle & in the distal part was completely fused with median nerve. On the other (right) side, the usual normal pattern of brachial plexus was seen. A knowledge of such variations is of interest to anatomists, clinicians, anesthesiologists and especially to the surgeons. These are of immense importance during surgical exploration of axilla and arm region and also during nerve block. It also helps clinicians in proper understanding of some previously unexplained clinical symptoms. The ontogeny, phylogeny & clinical significance of the entity are discussed in detail.