a rare anatomical innervation of the musculocutaneous nerve

a rare anatomical innervation of the musculocutaneous nerve m.m. taghavi msc , m. shariati kohbanani msc , s.m. seyedmirzaee md received: 24/09/06 sent for revision: 20/02/07 received revised manuscript: 07/04/07 accepted: 27/05/07 background and objectives: anatomically the musculocutaneous nerve (c5,6 ) is a branch of lateral cord of the brachial plexus and its motor nerve fibers innervates the muscles of anterior compartment of the arm. this nerve penetrates into the coracobrachialis of arm muscle and lies between biceps and brachialis muscles. at the lateral bicipital groove becomes superficial and the finally converts to lateral cutaneous nerve of the foream. here we report a rare case of musculocutaneous nerve variation. case report: we found a rare anatomical form of musculocutaneous nerve during upper left limb dissection of a male cropse who was in dissecting room of rafsanjan medical school. his body was tall with muscular limbs, weighed 65-75kg, 175 cm height, and fifty years old. the following variations were observed after dissecting of the axillary and arm regions. 1) the musculocutaneous nerve arised from the lateral root of the median nerve. 2) the coracobrachialis muscle was innervated by a branch of the lateral cord of the brachial plexus. 3) the musculocutaneous nerve did not penetrate into the coracobrachialis muscle but rather passed between the brachialis and biceps muscles. at the level of lateral bicipital groove, it then became a superficial nerve as the lateral cutaneous nerve of forearm. hense, it was very close to the brachial artery and median nerve in the upper one-third of arm. conclusion: this study describes a rare innervation of the musculocutanous nerve and requires further study to understand the nature of this unique structure. this atypical innervation is extremely important for surgical procedures performed on the arm muscles and adjecent vessels. key words: musculocutaneous nerve, variation, brachial plexus