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: 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 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 carotid sheath at the carotid bifurcation level. We report regression and correlation analyses for age, gender, height, weight and geographic continents.

RESULTS: We included 11 studies with 885 healthy volunteers (mean age 42.7 years) and 3,149 examined nerve sites. Calculated mean pooled CSA of C5 root was 5.6mm2 [95% confidence interval (95%CI):4.6-6.7mm2 , n=911], of C6 root 8.8mm2 (95%CI:7.4-10.3mm2 , n=909), of C7 root 9.5mm2 (95%CI:8.0-10.9mm2 ,n=909), of vagal nerve 2.2mm2 (95%CI:1.5-2.9mm2 , n=420). No heterogeneity was found across studies for any site. Subgroup analysis revealed no significant effects of age, gender, height, weight and geographic continents on CSA of any of these nerve sites.

CONCLUSION: 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 in all nerve sites. Our data facilitate the goal of an international standardized evaluation protocol.