Independent C5 And C6 Superior Trunks of The Brachial Plexus with An Anomalous Origin of The Pectoral Nerves

Background: The superior trunk of the brachial plexus provides innervation of the upper arm and shoulder regions, formed from nerve roots C5 and C6. The suprascapular nerve branches off the upper trunk, supplying innervation to the supraspinatus and infraspinatus muscles. Existing literature documents variations in the brachial plexus structures. Although the functional impact of these anomalies can vary, it is crucial to document them to expand on anatomical knowledge of the brachial plexus.
Methods: A unique variation of the superior trunk of the brachial plexus was discovered during a routine educational dissection in a male cadaver. The current authors present a case of a non-union of the C5 and C6 nerve roots at the upper trunk of the brachial plexus, along with variations in the structure and branching pattern of downstream nerves.
Discussion: While anatomical variations of the brachial plexus are not uncommon, anomalies of the upper trunk are not well documented. Specifically, variations in the C5 and C6 nerve roots can have effects such as plexopathies and other clinical disorders. Understanding these variations is particularly important for surgeons, as the upper trunk is a landmark during shoulder arthroscopy, rotator cuff repair, shoulder replacement surgery, and nerve blocks.
Conclusion: The current case report documents a variation of the upper trunk with the purpose of expanding current literature and understanding of anatomical variations within the brachial plexus. Due to the post-mortem nature of the current report, the scope is limited and there is no certainty regarding the effects of this anomaly on physiology.