Ultrasound reference values for peripheral nerve cross-sectional areas and indices in a sample of healthy individuals in Brazil

OBJECTIVE: To establish peripheral nerve cross-sectional area (CSA) reference values (absolute values, measures of asymmetry, and measures of focality) for healthy individuals in Brazil. MATERIALS AND METHODS: Sixty-six healthy volunteers underwent high-resolution ultrasound of the peripheral nerves. We obtained CSA measurements for three peripheral nerves, at specific locations: the median nerve, in the carpal tunnel (MT); the ulnar nerve, at the cubital tunnel site (UT) and at the pre-tunnel site (UPT); and the common fibular nerve, near the fibular head (FH). We calculated the CSA indices between the same sites on different sides (ΔCSAs) and between the ulnar nerve tunnel and pre-tunnel sites on the same side (ΔTPT). RESULTS: A total of 132 neural sites were analyzed, and the following CSA values (mean ± SD, median) were obtained: MT (6.3 ± 1.9 mm(2), 6.0 mm(2)); UT (6.2 ± 1.6 mm(2), 6.1 mm(2)); UPT (5.6 ± 1.7 mm(2), 5.4 mm(2)); and FH (10.0 ± 3.7 mm(2), 9.9 mm(2)). The ΔCSA values (mean ± SD, median) were as follows: MT (0.85 ± 0.7 mm(2), 0.95); UT (0.81 ± 0.62 mm(2), 0.95); UPT (0.61 ± 0.51 mm(2), 0.5); and FH (1.0 ± 0.77 mm(2), 1.0). The ΔTPT (mean ± SD, median) was (1.0 ± 0.8 mm(2), 1.0). CONCLUSION: Among individuals in Brazil, peripheral nerve CSA values tend to be higher among males and to increase with aging. However, the same does not appear to hold true for the ΔCSA or the ΔTPT, the exception being the difference between the right and left UT. Differences in CSA values greater than 2.5 mm(2) between sides or between sites along the same nerve can indicate asymmetry or focal thickening in neuropathy, respectively.