Unilateral absence of Casserio’s nerve and a communicating branch to the median nerve. An additional variant of brachial flexors motor innervation

Anomalies of the brachial plexus including the distribution of the nerves as well as its terminal branches in the upper limb have been largely described in the literature. In this case report we describe a further variant of brachial plexus formation identified during routine anatomical dissection of the right upper limb of a 62-year-old Caucasian female cadaver. On the right side no musculocutaneous nerve was identified, the median nerve was formed as expected but a short extra branch communicating between the lateral cord and the medial head of the median nerve appeared. Coracobrachialis muscle was innervated by a direct branch from the lateral cord, while biceps brachialis and brachialis muscles were reached by collaterals of the median nerve. Moreover, in the distal half of the upper limb, the median nerve contributed to the innervation of the lateral aspect of the forearm skin via the lateral cutaneous nerve of the forearm. In order to analyze this specific variant relevance we compared it with all the similar previous reported cases, trying to explain the embryological bases of the variant. The knowledge of anatomical variations of peripheral nerves is pivotal not only for surgeons, radiologists and anesthesiologists that may operate on the axilla, but also for every medical doctor to understand inexplicable clinical signs.