Anatomy of the accessory nerve and its cervical contributions in the neck.

Details of the course of the accessory nerve and the pattern of the cervical contributions to the nerve are essential for planning neck dissection. Based on a recent anatomic description, a technique was devised to preserve the distal accessory nerve; the theory advanced was that the trapezius was supplied by motor fibers from the cervical plexus, which join the accessory nerve in the posterior triangle. Dissections were performed on 23 cadavers to test such a theory. The course of the accessory nerve in the neck was mapped in each dissection, and landmarks for use during surgery determined. Cervical contributions to the nerve usually joined deep to the sternocleidomastoid, and not in the posterior triangle. Branches from the cervical plexus, independent of the accessory nerve, entered the trapezius in the posterior triangle. None of the bilateral dissections showed symmetry of the cervical contributions.