Quantitative MR imaging of carpal tunnel syndrome

OBJECTIVE, Previous MR imaging studies have produced evidence of changes to structures within the wrist believed to be associated with carpal tunnel s yndrome, In an attempt to resolve the conflicting and inconclusive results of these studies, we report here the results of an MR imaging study at a fi eld strength of 3.0 T, which is higher than that previously reported. SUBJECTS AND METHODS. Patients with carpal tunnel syndrome and control grou ps of asymptomatic subjects were studied using MR imaging. We evaluated ele ctrophysiologically the median nerve function of the affected wrists of all patients. A gradient-recalled echo pulse sequence was used to study 13 3-m m-thick slices within the wrist of each patient or asymptomatic subject. Sp atial resolution was approximately 0.3 x 0.3 mm(2). The median nerve and ot her structures associated with the carpal tunnel, which were clearly shown on the MR images, were analyzed to yield structural data. RESULTS. Analysis revealed that the cross-sectional area of the nerve withi n and proximal to the carpal tunnel was approximately 50% larger in patient s with carpal tunnel syndrome than in asymptomatic subjects. We found no si gnificant difference in the area of the nerve within the carpal tunnel comp artment compared with the area of the nerve proximal to the carpal tunnel e ither in patients or in asymptomatic subjects. Also, flattening of the nerv e on entering the carpal tunnel was not significantly different in patients than in asymptomatic subjects. In patients an increase in the palmar bowin g of the flexor retinaculum was found only at the level of the hamate compa red with that found in asymptomatic subjects. The cross-sectional area of t he carpal tunnel was of a similar size in patients and in asymptomatic subj ects. Comparison of electrodiagnostic results indicated no correlations bet ween the MR parameters and electrophysiologic dysfunction of the median ner ve for patients. CONCLUSION. The only statistically significant differences found between pa tients with carpal tunnel syndrome and asymptomatic subjects were that the median nerve was approximately 50% larger within and proximal to the carpal tunnel in patients with carpal tunnel syndrome and palmar bowing of the fl exor retinaculum occurred in patients only at the level of the hamate.