Rare anatomical variant of the spinal accessory nerve: case report and comprehensive review

Historical studies of the anatomy of the spinal accessory nerve (SAN) have reported conflicting results regarding its relationship with the internal jugular vein (IJV). A literature review was undertaken to establish the prevalence of anatomical variations of the SAN encountered during routine neck dissection surgery, in order to increase awareness and reduce morbidity associated with iatrogenic SAN injury. The published literature was analysed by qualitative synthesis and nine articles were yielded following application of the inclusion and exclusion criteria. Incidences of the SAN lateral to the IJV and medial to the IJV ranged from 39.8% to 96.6%, and 2.6% to 57.4%, respectively. Five of the studies reported incidences of the SAN traversing the IJV, which occurred in 0.9% to 2.8% of cases. One study reported an isolated variant of the SAN dividing around the IJV, with a prevalence of 0.5%. We present a case report demonstrating the rare variant of the SAN traversing the IJV. Preoperative identification of rare anatomical association of the SAN and IJV may reduce perioperative injury to vital structures during neck dissection.