To assess the value of high-resolution ultrasound in the etiological assessment of carpal tunnel syndrome (CTS).

Sixty-three patients (95 wrists) with CTS diagnosed by electrophysiological ?ndings or surgical operation were examined by ultrasonography from March 2015 to December 2019 at the Chinese PLA General Hospital. Ultrasound examinations were performed to assess the position, site of compression, fascicles, epineurium, and the surrounding structures of the median nerve. The cross section of the median nerve at the level of the pisiform bone was measured. Intraneural power Doppler signals were also evaluated. The t-test of independent samples was used to compare the difference of the cross section area between the symptomatic and contralateral asymptomatic wrists. Using the receiver operating characteristic (ROC) curve, the diagnostic value of the cross-sectional area of the median nerve at the pea bone plane was analyzed, and the best diagnostic boundary value was identified.

High-resolution ultrasound showed increased cross-sectional area, blurry structure of nerve bundles, and thickening of the epineurium of the median nerve in patients with CTS. Power Doppler ultrasound showed increased intraneural signals of the median nerve. There were significant differences in the cross section area of the median nerve at the level of the pisiform bone between the affected and asymptomatic wrists [(15.91±5.95) mm² vs (8.71±1.62) mm²; t=-2.51, P＜0.001]. The area under the ROC curve was 0.946. A cut-off point of 10.5 mm2 resulted in a sensitivity of 89.5% and specificity of 83.9%. The high frequency ultrasound diagnosed idiopathic carpal tunnel syndrome in 73 sides (76.8%, 73/95). A total of 22 wrists (23.2%, 22/95) could be clearly diagnosed, which included 13 cases (13.7%, 73/95) of flexor tendon tenosynovitis in the carpal tunnel, 1 case (1.1%, 1/95) of flexor tendon sheath effusion in the carpal tunnel, 2 cases (2.1%, 2/95) of carpal canal ganglion cyst, 1 case (1.1%, 1/95) of carpal canal solid mass, 2 cases (2.1%, 2/95) of superficial flexors of the fingers in the carpal tunnel, 2 cases (2.1%, 2/95) of upper bifurcation of the median nerve with persistent median artery, and 1 case (1.1%, 1/95) of distal radius postoperative scar compressing the median nerve.

High-resolution ultrasound is useful for assessing the etiology of CTS.