Differential age-, gender-, and side-dependency of vagus, spinal accessory, and phrenic nerve calibers detected with precise ultrasonography measures.

INTRODUCTION: The standard ultrasonographic measurement tools (trace, ellipse) of cross-sectional areas (CSAs) of very small nerves typically yield rough measures in full square millimeters. METHODS: In 70 volunteers, the elliptically shaped CSAs of mid-cervical vagus, accessory, and phrenic nerves were estimated with three methods: 2 on-board tools (area tracing, ellipse fitting) and an off-line calculation of the CSA after on-board measuring of its long-axis and short-axis diameters both displayed with 1-2 digits following the decimal point. RESULTS: CSA measures of all mid-cervical nerves obtained with the precise approach were smaller than the two standard measures (each P < 0.001). Larger CSA of right compared to left vagus nerve was detected with all methods. However, decrease of accessory and phrenic nerve CSAs with increasing age and larger size of vagus nerve CSA in women vs. men were evident only with precise measures. DISCUSSION: Small nerve CSA should preferably be estimated with precise measures. Muscle Nerve 59:486-491, 2019.