Comparing the Carpal Tunnel Area and Carpal Boundaries in Patients with Carpal Tunnel Syndrome and Healthy Volunteers: A Magnetic Resonance Imaging Study

Background: Carpal tunnel syndrome (CTS) is a common neuropathy caused by compression of the median nerve (MN) within the carpal tunnel, which causes pain, paresthesia, or altered sensation. While a small carpal tunnel area is considered a risk factor for CTS, varying carpal tunnel dimensions in CTS patients have been obtained via axial computed tomography and magnetic resonance imaging (MRI). Methods: In this retrospective study, MR images from 49 CTS patients and 38 healthy controls were analyzed to investigate differences in the carpal tunnel area and carpal boundaries between the groups and to explore the relationships of these parameters with CTS severity. Results: Our findings revealed that compared with the controls, CTS patients presented significantly larger cross-sectional areas (CSAs) of the MN and carpal tunnel and increased MN flattening ratios. The CSAs of the MN showed moderate positive correlations with severity (r = 0.395, p < 0.001), symptom score (r = 0.354, p < 0.001), and disability score (r = 0.300, p < 0.001), while the carpal tunnel area showed weaker but significant correlations with severity (r = 0.268, p = 0.002), symptom score (r = 0.173, p = 0.026), and disability score (r = 0.183, p = 0.018). The ratios of the MN CSA to those of the carpal tunnel, the interior carpal boundary (ICB), the exterior carpal boundary (ECB), and the wrist were disproportionately greater in the CTS patients. Among them, both the MN-to-ICB and MN-to-ECB ratios had fair to good diagnostic values (area under the curve = 0.725 and 0.794, respectively). Conclusions: These results highlight the utility of MRI-derived CSA measurements and ratios in identifying pathophysiological changes in CTS patients, particularly crowding of the MN inside the carpal tunnel. Further studies are recommended to refine MRI-based diagnostic protocols for CTS.