Coexistence of Brachial Plexus-Anterior Scalene and Sciatic Nerve-Piriformis Variants

The trunks of the brachial plexus typically pass through the interscalene triangle, between the anterior and middle scalene muscles and superior to the first rib. Likewise, the two components of the sciatic nerve, tibial and common fibular nerves, usually join and pass together inferior to the piriformis muscle. We present a cadaver with anatomic variations of both the right brachial plexus-interscalene triangle relationship and the sciatic nerve-piriformis relationship. The right brachial plexus C5 and C6 roots formed the superior trunk as they passed through a bifurcated anterior scalene muscle, while the C7, C8, and T1 roots passed posterior to the anterior scalene. After passing through the left greater sciatic foramen, the sciatic nerve branched into the common fibular and tibial nerves, which passed through and inferior to the piriformis muscle, respectively. The presence of these anatomic variations may predispose individuals to symptomatic nerve entrapments such as thoracic outlet syndrome and piriformis syndrome. This finding is relevant to clinicians performing invasive procedures and diagnosing neurological conditions.