Anatomical variations in the relationship between the spinal accessory nerve and internal jugular vein: a systematic review and meta-analysis.

The relationship between the spinal accessory nerve and internal jugular vein is important for modified neck dissection surgery. Therefore, the aim of this review was to investigate variations in this relationship. Through a search of the PubMed, Scopus, Web of Science, LILACS, and SciELO databases, the review authors collected anatomical data for inclusion in a meta-analysis, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Four relationship patterns were identified and classified: type 1, the nerve lies superficial to the vein; type 2, the nerve lies deep to the vein; type 3, the nerve crosses the branches of the vein; type 4, the nerve splits and its branches pass around the vein. The last pattern was not included in the meta-analysis. Eighteen studies were included (useful sample of 1491 hemi-necks). Type 1 variation had a prevalence of 79.7% (95% CI 77.6-81.7%), type 2 had a prevalence of 19.6% (95% CI 17.7-21.7%), and the type 3 had a prevalence of 0.7% (95% CI 0.0-1.4%). Significant differences were found among geographical subgroups. Normally, the spinal accessory nerve passes superficial to the internal jugular vein, but anatomical variations are common and there is a geographical influence. These findings are important for the safety of modified radical neck dissections.