Carpal tunnel syndrome: correlation of magnetic resonance imaging, clinical, electrodiagnostic, and intraoperative findings.

We undertook a prospective study of 43 wrists in 32 patients who had been clinically diagnosed as having carpal tunnel syndrome (study group) and 5 wrists in people who had no symptoms (control group), correlating the clinical, electrodiagnostic, intraoperative, and magnetic resonance imaging (MRI) findings. MRI of the carpal tunnel and thenar eminence was performed, using coronal and axial T1- and T2-weighted, proton density, and short tau inversion recovery sequences. Abnormalities of the median nerve, as revealed by MRI, were found in 43 of 43 (100%) wrists in the study group and in 0 of 5 (0%) wrists in the control group. Increased signal of the median nerve was seen in 41 of 43 (95%) wrists, increased signal of the flexor tendon sheath in 41 of 43 (95%), volar bowing of the flexor retinaculum in 39 of 43 (91%), increased distance between the flexor tendons in 37 of 43 (86%), and abnormal nerve configuration in 28 of 43 (65%). Increased short tau inversion recovery signal of the thenar muscles was found in 5 of 43 (12%) wrists, all of which had undergone severe denervation changes, as revealed by electromyography. Operative release was performed for 27 of 43 (63%) wrists, and follow-up was obtained for 42 of 43 (98%). A good or excellent postoperative outcome resulted for 20 of 27 (74%) patients, a fair outcome for 2 of 27 (7%), and a poor outcome for 4 of 27 (15%), and 1 of 27 (4%) patients was lost to follow-up. For patients undergoing carpal tunnel release whose MRI revealed an abnormal nerve configuration, the outcome was improved, with good or excellent results in 15 of 18 (83%) patients. No association with outcome was seen with median nerve or flexor tendon signal changes, increased interspace between the flexor tendons, or flexor retinaculum bowing. Our results indicate that MRI is a sensitive diagnostic modality that can demonstrate signal and configurational abnormalities of the median nerve in patients diagnosed with carpal tunnel syndrome. Increased signal of the thenar muscles, as revealed by MRI, using short tau inversion recovery sequences, occurs only in muscles that have undergone severe denervation changes, as revealed by electromyography.