Ultrasonographic normative reference values for median nerve cross-sectional area in healthy Nigerian women of reproductive age

Abstract Background Ultrasonographic measurement of median nerve cross-sectional area (CSA) is widely used in evaluating carpal tunnel syndrome (CTS). Accurate interpretation requires population-specific normative values, which remain limited for African populations, particularly women. This study established normative reference values for median nerve CSA in healthy Nigerian women of reproductive age and evaluated associations with anthropometric variables. Methods This prospective cross-sectional study included 165 healthy, asymptomatic, non-pregnant women aged 18–49 years. Bilateral median nerve CSA was measured using a 6–12 MHz linear transducer at the carpal tunnel inlet (pisiform level) and 5 cm proximal to the distal wrist crease. All ultrasound examinations were performed by a single experienced radiologist. Measurements were calculated using the ellipsoid formula, with three readings obtained at each site and the mean value recorded for analysis. Paired t-tests assessed side-to-side differences, and Pearson correlation evaluated associations with age and body mass index (BMI). Statistical significance was set at p < 0.05. Results Mean age was 32.08 ± 6.73 years; mean BMI was 25.52 ± 5.30 kg/m 2 (47.9% normal, 30.9% overweight, 19.4% obese). At the carpal tunnel inlet, mean CSA was 8.17 ± 2.65 mm 2 on the right (95th percentile: 13.73 mm 2 ) and 7.84 ± 2.34 mm 2 on the left (95th percentile: 12.36 mm 2 ). Proximally, mean CSA was 6.56 ± 1.90 mm 2 on the right (95th percentile: 9.50 mm 2 ) and 6.42 ± 2.14 mm 2 on the left (95th percentile: 9.98 mm 2 ). Side-to-side differences were not significant ( p = 0.053 at carpal tunnel inlet; p = 0.176 proximally). Weak negative correlations were observed between CSA and age and BMI (all p > 0.05). Conclusion This study provides normative reference values for median nerve CSA in Nigerian women. The reported 95th percentile values may serve as provisional upper reference limits; however, further clinical and electrodiagnostic validation is required to establish definitive diagnostic cut-offs for CTS.