MR imaging of the carpal tunnel

Investigations were conducted regarding changes of carpal tunnel shape during wrist motion and the variations of space for the median nerve as well as the preoperative signs of carpal tunnel syndrome (CTS) and the postoperative restitution.

Axial MR images (1.0 T) were performed at the level of the distal radioulnar joint, pisiforme bone and hook of hamate level of 20 wrists of patients with clinical symptoms of CTS and further 20 wrists of volunteers. This was conducted with the wrist in neutral position, 45 degrees extension and 45 degrees flexion. T2-weighted signal intensity of the median nerve were measured in 18 patients pre- and postoperatively.

The increase of the cross-sectional area of the median nerve at the pisiform level and the flattening of the median nerve at the hook of hamate level as well as the volar bowing of the flexor retinaculum at the pisiform and hook of hamate level were significantly greater in patients with CTS than in those with normal wrists (P < 0.05-0.001). In postoperative follow-up studies the distal flattening of the median nerve recovered in 94%. The signal intensity of the median nerve on T2-weighted images decreased in 67%.

Flexion at the pisiform and hamate level as well as extension at the pisiform level narrows the space available for the median nerve potential leading to compression of the median nerve. MR imaging is accurate and reliable for diagnosis and postoperative follow-up of CTS.