Potential MR signs of recurrent carpal tunnel syndrome: initial experience

In nonoperated patients, the MR diagnosis of carpal tunnel syndrome (CTS) is difficult. In the postoperative patient this difficulty is compounded. Consequently, we sought to evaluate for potential MR signs of postoperative CTS. At 1.5 T, 41 wrists in 37 patients with previous CTS release were evaluated by two observers for 1) flexor retinacular regrowth; 2) median nerve: a) high T2 signal, b) proximal enlargement, c) fibrous fixation, d) neuroma, and e) entrapment; 3) flexor tenosynovitis; 4) mass, bursitis, accessory muscle, distal belly progression, or excessive deep fat; 5) hamate fracture; and 6) volar nerve migration. Electromyography (EMG), operative findings, and clinical follow-up were used to determine the presence of recurrent CTS. Fifteen of 41 wrists had recurrent CTS. Retinacular regrowth was seen in 4/15 (27%) with and 7/26 (27%) without recurrent CTS (P=0.7). Excessive fat was seen in 1/15 (7%) with and 2/26 (8%) without CTS (P=0.19). No patient had incomplete resection of flexor retinaculum, scarring, neuroma of nerve, or tendon laceration; bursitis, accessory or distal muscle progression of muscle belly, or hamate fracture. Nerve edema with high T2 signal was seen in 4/15 (27%) with and 3/26 (12%) without CTS (P=0.16); proximal enlargement was seen in 6/15 (40%) with CTS and 2/26 (8%) without CTS (P=0.007). Also, 1 patient with recurrent disease demonstrated a mass and 1 other patient without CTS had nerve entrapment. Tenosynovitis was seen in 9/15 (60%) with and 9/26 (35%) without recurrent CTS (P=0.02). Counterintuitively, the nerve was more palmar with recurrent CTS than without (mean 6.9/8.9 mm). Only proximal enlargement, tenosynovitis, and the rare mass may help to diagnose recurrent CTS by MR. However, there appears to be a subgroup of patients with recurrent neuropathy related to an excessively superficial median nerve.