Intraoperative relationship of the spinal accessory nerve to the internal jugular vein: Variation from cadaver studies

Purpose Conflicting locations of the spinal accessory nerve (SAN) with respect to the internal jugular vein (IJV) are reported in the literature and anatomy texts. The objective of this study is to analyze this anatomic relationship specifically at the level of the posterior belly of the digastric muscle where it is encountered most often during surgery. Material and Methods This study is a case series with planned chart review of all operative reports for neck dissections/explorations performed between June 2002 to June 2008 at an academic tertiary care referral center. Inclusion criteria required intraoperative identification of the SAN at the level of the posterior belly of the digastric muscle. Patients undergoing revision neck dissection were excluded. Data is presented using descriptive statistics. Results One hundred ninety-seven patients were identified; 175 met inclusion criteria. Thirty-two patients received bilateral neck dissections/explorations, resulting in a total of 207 SANs for analysis. The most common location of the SAN was lateral to the IJV (198; 95%). In 6 (2.8%) cases the SAN was identified medial to the IJV and 2 nerves pierced the IJV. A new variant of the SAN splitting around the SAN was identified. Conclusion The majority of SANs course lateral to the IJV at the level of the posterior belly of the digastrics muscle (95%). This intraoperative finding differs from cadaveric studies. Discrepancies may reflect variation in the level at which the nerve was identified, as well as tissue changes related to cadaver versus in vivo studies.