Cross-sectional area reference values for peripheral nerve ultrasound in adults: A systematic review and meta-analysis-Part III: Cervical nerve roots and vagal nerve.

BACKGROUND AND PURPOSE: Measurement of the cross-sectional area (CSA) of cervical nerve roots using ultrasound is useful in the evaluation of inflammatory polyneuropathies, and measurement of CSA of the vagal nerve might give information about involvement of the autonomic nervous system. We performed a systematic review and meta-analysis of published CSA reference values for cervical nerve roots and vagal nerve. METHODS: We included available-to-date nerve ultrasound studies on healthy adults and provide meta-analysis for CSA of the following nerves: cervical nerve roots C5, C6, and C7 as well as vagal nerve in the carotid sheath at the carotid bifurcation level. We report regression and correlation analyses for age, gender, height, weight, and geographic continent. RESULTS: We included 11 studies with 885 healthy volunteers (mean age = 42.7 years) and 3149 examined nerve sites. Calculated mean pooled CSA of C5 root was 5.6 mm2 (95% confidence interval [CI] = 4.6-6.7 mm2 , n = 911), of C6 root was 8.8 mm2 (95% CI = 7.4-10.3 mm2 , n = 909), of C7 root was 9.5 mm2 (95% CI = 8.0-10.9 mm2 , n = 909), and of vagal nerve was 2.2 mm2 (95% CI = 1.5-2.9 mm2 , n = 420). No heterogeneity was found across studies for any site. Subgroup analysis revealed no significant effects of age, gender, height, weight, and geographic continent on CSA for any of these nerve sites. CONCLUSIONS: We provide the first meta-analysis on CSA reference values for the cervical nerve roots and the vagal nerve, with no heterogeneity of reported CSA values at all nerve sites. Our data facilitate the goal of an international standardized evaluation protocol.