Surgical anatomy of the spinal accessory nerve and the trapezius branches of the cervical plexus

Background: A thorough understanding of the topographical anatomy of the sp inal accessory nerve and the cervical plexus branches is a basic prerequisi te for positive results when operating on the neck. Objective: To give an exact description of the topographical and surgical a natomy of the spinal accessory nerve (SAN) and the trapezius branches of th e cervical plexus. Design: Anatomic analysis of the SAN and the trapezius branches of the cerv ical plexus. Setting: The topographical anatomy of the SAN and the cervical plexus branc hes were studied in the anterior and posterior triangles of the necks of 46 perfusion-fixed human cadavers of both sexes, which ranged in age from 55 to 97 years (mean age, 83 years). Results: The SAN can be identified on the posterior border of the sternocle idomastoid (SCM) muscle, 8.2+/-1.01 cm cranial to the clavicle. In 37% of c ases, the SAN enters the posterior triangle of the neck dorsal to the SCM m uscle, where it passes through the muscle in 63% of these cases. In the ant erior triangle of the neck, the SAN crosses the internal jugular vein ventr ally in 56% of the cases and dorsally in 44%. Regarding the cervical plexus , 1 trapezius branch could be found in 9% of the specimens, 2 in 61%, and 3 in 30%. None of the branches merged with the SAN medial to the anterior bo rder of the trapezius muscle. In most cases, a tiny additional branch could be found arising from the SAN about 2 cm medial to the trapezius muscle. T his branch enters the descendant part of the muscle approximately 2 to 3 cm cranial to the main nerve. Conclusions Surprisingly, available data on topographical as well as surgic al anatomy of the SAN and the trapezius branches of the cervical plexus are confusing and often wrong. The descriptions given herein can help to minim ize the risk of injuring the SAN during neck surgery and preserve the addit ional innervation of the trapezius muscle granted by the rami trapezii of t he cervical plexus.