Study of the Anatomical Variations of Spinal Accessory Nerve Seen During Neck Dissection

In our study, thirty one neck dissections in thirty patients were performed as a part of their treatment for head and neck cancers over a period of one year. In this study, we aimed to report anatomical variations of the spinal accessory nerve (SAN) encountered during neck dissection with respect to important reference points and structures in the neck and correlate them with the length of the neck and height of patient. We preserved SAN in all the neck dissections and studied its course and branching in relation to internal jugular vein (IJV), sternocleidomastoid (SCM) muscle, greater auricular point (GAP), mastoid process, clavicle, angle of mandible, length of the neck and height of the patient. In 67.7% patients, the SAN was ventral to the IJV at the level of posterior belly of digastric muscle and in 32.3%, it was dorsal to the vein. In all the cases, SAN was found cephalic to the GAP at the posterior border of the SCM muscle with a mean distance of 1.72 ± 0.54 cm (range 0.90-3.06 cm). The distance between the tip of mastoid process and the point of emergence of the SAN from the posterior border of SCM (Exit Point length) was found to be nearly constant with a mean of 6.35 ± 0.63 cm (range 5.03-8.13 cm). We also found that there is a positive correlation between various parameters and the length of the neck and height of patients. Distance of exit point of SAN from the clavicle, however, is least helpful. We infer that the GAP is one of the most reliable landmarks for the localization of the SAN, followed by distance of exit point from mastoid process and angle of mandible. Also, surgeon should be aware of the variations regarding relationship to internal jugular vein and branching pattern of the nerve. The exit point should be sought for relatively inferiorly in longer necks and taller patients. SAN has great variations and thorough knowledge of these helps to prevent debilitating sequelae and medicolegal repercussions of shoulder syndrome.