Complex Branching Patterns of the Left Brachial Plexus: A Case Report of Five Concurrent Anatomical Variations.

Background: Anatomical variations of the brachial plexus are common and may significantly influence surgical approaches, regional anaesthesia, and the interpretation of peripheral nerve injuries. Variations involving the musculocutaneous nerve and its relationship with the median nerve are particularly important given their clinical implications. Case presentation: During a routine surgical anatomy dissection course on a formalin-fixed adult male cadaver, a rare variation was identified in the left upper limb. A 4 cm common trunk arising from both the medial and lateral cords of the brachial plexus bifurcated into the median and musculocutaneous nerves. The musculocutaneous nerve did not pierce the coracobrachialis muscle but supplied it via an accessory branch, with an additional branch arising directly from the lateral cord. A distal communicating ansa brachialis between the musculocutaneous and median nerves was also observed. Conclusion: This case highlights a rare median-musculocutaneous trunk with associated neural communications and atypical muscular innervation. Awareness of such variations is essential for clinicians involved in upper limb surgery, peripheral nerve repair, and regional anaesthesia, as they may alter expected anatomical landmarks, influence surgical strategies, and affect clinical outcomes.