The Inlet Cross-Sectional Area: The Most Reliable Ultrasound Parameter for the Diagnosis of Carpal Tunnel Syndrome.

Abstract

Despite emerging interest in dynamic parameters like the ratio of median nerve-to-hamate distance (RMHD) for diagnosing carpal tunnel syndrome (CTS)-particularly in selected populations such as hemodialysis patients-this study evaluates whether the inlet cross-sectional area (CSA-I) retains diagnostic superiority in a general CTS population. In this case-control study, 88 participants (44 CTS patients, 44 healthy controls) were recruited from a tertiary referral university hospital between November 2024 and March 2025. High-resolution ultrasonography measured median nerve parameters. Diagnostic accuracy (AUC, sensitivity, specificity) of CSA-I vs. Outlet cross-sectional area (CSA-O), anteroposterior diameters (AP-I/O), flattening ratio at the outlet (FR-O), and RMHD during rest/grip. CSA-I demonstrated exceptional diagnostic accuracy (AUC = 0.93). At a cutoff of >9.5 mm2, CSA-I yielded 86% sensitivity and 84% specificity. CSA-O showed lower accuracy (AUC = 0.88) and novel dynamic parameters such as RMHD performed poorly in this general population (AUC ≈ 0.50). CSA-I remains the most reliable sonographic parameter for diagnosing CTS in the general population. A CSA-I value >9.5 mm2 is recommended for routine clinical practice. Dynamic measures may retain value in specific subgroups but do not replace CSA-I for general CTS evaluation.