Accessory nerve: anatomy and surgical identification.

The XIth cranial nerve or accessory nerve provides the motor supply to the sternocleidomastoid and trapezius muscles. It is frequently encountered during neck surgery, and as such is at risk of iatrogenic injury, resulting in the 'shoulder syndrome'. Historically, the nerve was sacrificed on oncological grounds during radical neck dissection. However, the basis for sacrifice is unfounded in the majority of cases, and accessory nerve sparing selective neck dissection has equal oncological efficacy. The path of the nerve in the neck is very variable, and there is not a wholly reliable landmark for its identification. However, there are a number of methods described in the literature to guide the surgeon in its identification. This paper provides a systematic review of all the methods available for identification of the accessory nerve, and comments on the reliability of each. In doing so, the detailed anatomy of the accessory nerve is also described.