Atypical branching of the musculocutaneous and median nerves with associated unusual innervation of muscles in the anterior compartment of the arm: case report and plea for extension of the current classification system

Purpose Variations of the peripheral nervous system in the upper limb, especially of the musculocutaneous and median nerves, are common, but closer attention to the knowledge of the variant anatomy should be paid to avoid iatrogenic injury or to understand the unusual clinical signs. Methods During a routine dissection course, bilateral variations were observed in a Central European male cadaver. Results Variable branching of the musculocutaneous and median nerves associated with atypical innervation of the muscles in the anterior compartment of the arm and other concomitant variations were found bilaterally. In both cases, the musculocutaneous nerve innervated only the coracobrachialis muscle and terminated inside the muscle belly. Branches to the biceps brachii and brachialis muscles arose either directly from the median nerve or its branches. On the right side, two communicating branches between the roots of the median nerve were noted, and a common medial cutaneous trunk originated from the lateral cord. On the left side, a communicating branch extended from the lateral cord to the medial root of the median nerve and a tributary to the axillary vein passed through a window formed by the roots of the median nerve and the communicating branch. Conclusion There exist only few cases in the literature describing similar variations, but the present arrangement has not yet been reported to the best of our knowledge. With the proposed extension to the existing classification system, we aim to provide clearer orientation in the variability of the musculocutaneous and median nerves.