Ultrasonographic Reference Values of the Brachial Plexus Cross‐Sectional Area in Healthy Japanese Adults

Introduction/Aims The availability of reference cross‐sectional area (CSA) values for the brachial plexus in healthy Japanese individuals and their relationship with physical characteristics remains limited. This study aimed to determine ultrasonographic reference CSA values of the brachial plexus and to examine their relationship with physical characteristics. Methods CSA measurements were performed at the nerve roots (C5–Th1), nerve trunks, and total cord (TC) of 60 healthy Japanese adults. Physical characteristics were measured, and statistical analyses assessed their relationships with the CSA. Results The CSA values differed by anatomical level. At the nerve root level, the CSA of C7 was the largest (mean 9.5 ± standard deviation 2.2 mm 2 ), while the CSAs of C5 (4.7 ± 1.3 mm 2 ) and Th1 (5.2 ± 1.3 mm 2 ) were the smallest. At the nerve trunk level, the CSA of the upper trunk (19.9 ± 3.2 mm 2 ) was larger than that of the middle trunk (13.1 ± 2.4 mm 2 ). The CSA of TC was 73.7 ± 12.2 mm 2 . Age, body mass index (BMI), and wrist circumference correlated with several CSAs, but no single characteristic was significantly associated with all the CSAs. The coefficients of variation ranged from approximately 20% to 30%. Discussion The site‐specific reference values presented in this study may be useful for the clinical interpretation of brachial plexus enlargement. While the BMI and wrist circumference influence the CSAs of the nerve trunk and TC, measurement errors must be carefully considered.