A novel case of multiple variations in the brachial plexus with the middle trunk originating from the C7 and C8

The brachial plexus is an important nervous structure from which all major nerves to the upper limb arise. It typically originates from the anterior rami of the C5-T1 spinal nerves. As it passes laterally, the roots are successively organized into three trunks, six divisions, and three cords. The BP is susceptible to injury during the perinatal and postnatal periods, as well as in adulthood. Its structure can show considerable variation, and there is a wealth of literature describing its variations, providing indispensable information to neurosurgeons. Here, we report a novel unilateral variant of the brachial plexus found in an adult Japanese male cadaver. In this case, the middle trunk arose from the C7 and C8 spinal nerves, and the inferior trunk continued from the T1 alone. At the interscalene triangle, the subclavian artery was situated between the C8 and T1 nerves. The posterior cord arose from the posterior divisions of the superior and middle trunks, while the root from the T1 nerve/inferior trunk was absent. The anterior division of the middle trunk gave independent roots to the musculocutaneous and median nerves, without completely establishing the lateral cord. A communicating branch arose from the musculocutaneous nerve to join the median nerve. Some branches from the roots and cords also deviated from typical configurations. This case represents a rare combination of variations in the trunks, divisions, cords, and the median nerve and offers a valuable addition to the literature regarding variations in the brachial plexus.