Quantitative MRI of the wrist and nerve conduction studies in patients with idiopathic carpal tunnel syndrome.

OBJECTIVE To correlate morphological findings of idiopathic carpal tunnel syndrome (CTS) with the function of the median nerve. METHODS In this study, 105 wrists of 105 women patients with idiopathic CTS, and 36 wrists of 36 female volunteers were subjected to nerve conduction studies and MRI. Cross sectional area, signal intensity ratio, and the flattening ratio of the median nerve, carpal tunnel area, flexor tendon area, synovial area, and intersynovial space, and the palmar bowing of the transverse carpal ligament (TCL) were quantified by MRI and correlated with the severity of the disease determined by nerve conduction studies. RESULTS Cross sectional areas of the median nerve, flexor tendons, and carpal tunnel, and the palmar bowing of the TCL of the CTS groups were greater than in the control group, but differences were not detected among the CTS groups for the area of the flexor tendons and the carpal tunnel. Enlargement, flattening, and high signal intensity of the median nerve at the distal radioulnar joint level were more significant in the advanced than in the earlier stages of the disease. Increase in palmar bowing of the TCL was less prominent in the most advanced group. Linear correlation between the area of the carpal tunnel and palmar bowing of the TCL was noted. CONCLUSION Severity of the disease could be judged by evaluating not only longitudinal changes of signal intensity and configuration of the median nerve, but also palmar bowing of the TCL. Increased palmar bowing of the TCL was found to be associated with an increase in the area of the carpal tunnel.