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 mm 2 and 24.4 mm 3 to 16.5 mm 2 and 18.1 mm 3 , 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 mm 2 and from 10.9 to 13.5 mm 3 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.