A systematic review: normative reference values of the median nerve cross-sectional area using ultrasonography in healthy individuals

Abstract

Median nerve cross-sectional area (CSA) was used for screening and diagnosis of neuropathy, but few studies have suggested reference range. Hence, this systematic review was performed to evaluate a normative values of median nerve CSA at various landmarks of upper limb based on ultrasonography. PubMed and Web of science were used to search relevant articles from 2000 to 2020. Forty-one eligible articles (2504 nerves) were included to access median nerve CSA at different landmarks (mid-arm, elbow, mid-forearm, carpal tunnel (CT) inlet and CT outlet). Data was also stratified based on age, sex, ethnicity, geographical location, and method of measurement. Random effects model was used to calculate pooled weighted mean (95% confidence interval (CI), [upper bound, lower bound]) at mid-arm, elbow, mid-forearm, CT inlet and outlet which found to be 8.81 mm2, CI [8.10, 9.52]; 8.57 mm2 [8.00, 9.14]; 7.07 mm2 [6.41, 7.73]; 8.74 mm2 [8.45, 9.03] and 9.02 mm2 [8.08, 9.95] respectively. Median nerve CSA varies with age, geographical location, and sex at all landmarks. A low (I2 < 25%) to considerable heterogeneity (I2 > 75%) was observed, indicating the variation among the included studies. These findings show that median nerve CSA is varying not only along its course but also in other sub-variables.

Potential Relationships between the Median Nerve Cross-Sectional Area and Physical Characteristics in Unilateral Symptomatic Carpal Tunnel Syndrome Patients

“…US on median nerve CSA have been compared between healthy controls and patients with peripheral neuropathy. A systematic review reported a mean normative reference value of 8.74 mm 2 for median nerve CSA at the CT entrance, which is approximately the same site as the wrist crease assessed in the present study (n = 1863) [ 29 ]. Furthermore, the systematic review found no correlation between age or sex and reported a value for median nerve CSA at the CT inlet that appeared to be similar between each region.…”

“…On the other hand, individual and site-specific differences in median nerve CSA were not small. Among studies measuring normal median nerve CSA at the CT inlet level, individual values widely ranged between 7 and 10 mm 2 (lower and upper bounds of 95% CI, respectively) [ 29 ]. Nakamichi et al measured the median nerve CSA of CTS patients at three different levels (the distal edge of the flexor retinaculum, the hook of the hamate, and at the wrist crease) and suggested that the median nerve had an hourglass-like shape [ 30 ].…”

Sonographic evaluation of median nerve cross‐sectional area in a normal Iranian population: A cross‐sectional study

“…In the present study, the largest diameter was observed at CTO. Evidently, MNCSA has its largest diameter at the level of the hamate bone (CTO) 6 …”

“…In the most recent review, the mean MNCSA was 8.81 mm 2 at mid-arm, 8.57 mm 2 at the elbow, 7.07 mm 2 at midforearm, 8.74 mm 2 at CTI, and 9.02 mm 2 at CTO. 6 Another study reported normal MNCSAs to be 8.2 mm 2 at the level of the radiocarpal joint, 8.3 mm 2 at CTI, and 8.1 mm 2 at CTO. 7 A handful of studies have provided reference values for MNCSA in certain sample populations.…”

Median Nerve Assessment With Ultrasonography: Cross-Sectional Area Measurements Preoperatively and Postoperatively in a Patient With Bilateral Carpel Tunnel Syndrome

“…Those parameters were not investigated and could have influence on MN thickness. 22 In addition, US is an operator-dependent test, and appropriate experience is required to ensure reproducibility. There were no data collected on interobserver or intraobserver variability.…”