Carpal tunnel syndrome. MR imaging diagnosis.

Carpal tunnel syndrome is a common condition that is often diagnosed by careful history and physical examination. Symptoms from cervical disc disease, thoracic outlet syndrome, and more proximal entrapment syndromes of the median nerve may be confused clinically with carpal tunnel syndrome. Incision of the flexor retinaculum in these patients will not relieve the symptoms, because the locus of the entrapment is not in the carpal tunnel. Electrophysiologic studies are invasive, painful, and may be equivocal on occasion. Furthermore, they provide little information into the cause of carpal tunnel syndrome. MR imaging is the best modality to image the carpal tunnel. It can define the locus of entrapment to the carpal tunnel. Findings includes swelling of the median nerve just proximal to the carpal tunnel, flattening of the nerve within the carpal tunnel, bowing of the flexor retinaculum, and increased signal intensity of the median nerve. Etiologic findings can differentiate space occupying lesions from diffuse inflammatory causes, and this may aid in management. Also, the signal characteristics of soft-tissue masses may be diagnostic. Knowledge of the course of the median nerve may be helpful when planning corticosteroid injection or surgery, especially with the endoscopic technique. MR imaging also may serve a role in postoperative evaluation of patients with recurrent symptoms by demonstrating an incomplete release of the flexor retinaculum or healing of an incised retinaculum. These unique abilities of MR imaging makes it a useful diagnostic tool not only for the initial evaluation and management but also in the postoperative evaluation of patients with carpal tunnel syndrome.