Visualization of the morphological changes in the median nerve after carpal tunnel release using three-dimensional magnetic resonance imaging

Objectives: This study aimed to compare the pre- and postoperative morphology of the median nerve using three-dimensional (3-D) MRI in patients with carpal tunnel syndrome (CTS). Methods: We assessed 31 patients with CTS who underwent open carpal tunnel release and T2*-weighted MRI of the wrist preoperatively and at 6 months postoperatively. The median nerve morphology was evaluated on the basis of the cross-sectional areas (CSAs) and cross-sectional volumes (CSVs). The association between these MRI findings and nerve conduction studies was also evaluated. Results: The mean preoperative CSA and CSV values at the proximal carpal tunnel level significantly decreased from 22.2 mm² and 24.4 mm³ to 16.5 mm² and 18.1 mm³, respectively, postoperatively. Median nerve swelling at the proximal carpal tunnel level was observed in 29 (94%) and 23 (74%) patients before and after surgery, respectively. The mean preoperative CSA and CSV values at the hamate level significantly increased from 9.9 to 12.3 mm² and from 10.9 to 13.5 mm³ after surgery, respectively. Nerve narrowing at the hamate bone level was preoperatively observed in 28 (90%) patients and postoperatively in 21 (68%) patients. Preoperative CSA and CSV values at the proximal carpal tunnel were significantly associated with preoperative distal motor and sensory latency. Conclusions: Visual confirmation of the median nerve morphology using 3-D MRI is useful when considering postoperative recovery and explaining the nerve condition to the patients. Key Points: • The 3-D morphology of the median nerve after carpal tunnel release can be delineated using 3-D MRI. • Preoperative swelling of the median nerve in the 2-D and 3-D planes reflects the severity of carpal tunnel syndrome. • Visual confirmation of the median nerve morphology is useful when considering median nerve recovery after carpal tunnel release and for explaining the condition of the nerve to patients.