Prevalence and characteristics of vagus nerve variations on neck ultrasonography

PURPOSE We aimed to evaluate the true prevalence and characteristics of vagus nerve (VN) variations using the carotid artery (CA) and the internal jugular vein (C-I axis). METHODS We examined patients who underwent neck ultrasonography (US) conducted by a single operator. A VN variation was defined as a VN located anterior or medial to the C-I axis. The subtypes of VN variation were classified as anterolateral, anteromiddle, anteromedial, and medial based on the relative location of the VN to the CA. The primary outcome parameters were the prevalence of VN variations and differences according to side, age, and sex. RESULTS Out of 536 patients, right and left VN variations were identified in 20 (3.7%) and 186 (34.7%), respectively (P<0.001). The anteromiddle type was the commonest type observed on both sides. Eight right (1.5%) and 50 left VNs (9.3%) were located <2 mm from the lateral border of the ipsilateral thyroid gland (P<0.001). The prevalence of VN variations in male and female patients was 42.1% and 32.7%, respectively (P=0.029), and that in patients aged <20, 20-39, 40-59, and ≥60 years was 23.8%, 22.5%, 34.4%, and 47.4%, respectively (P<0.001). CONCLUSION Variations in the VN position were relatively common on US. The variations primarily involved the left VN in the lower cervical region, and an increasing prevalence with age was observed.