Ultrasound of Carpal Tunnel Syndrome

In this radiology lecture, we review the ultrasound appearance of carpal tunnel syndrome!

Key teaching points include:

Most common upper extremity entrapment neuropathy. Results from median nerve compression
With carpal tunnel syndrome, see hypoechoic enlargement of the median nerve as enters carpal tunnel with flattening of nerve = Notch sign, also volar bowing of flexor retinaculum
Median nerve area: Less than 8 mm2 = Normal; 8-12 mm2 = Borderline; greater than 12 mm2 = Abnormal
Most accurate to compare nerve area at proximal pronator quadratus muscle and carpal tunnel: Increase of 2 mm2 or more from proximal to distal = 99% sensitive and 100% specific for carpal tunnel syndrome. Measure inside the echogenic epineurium
Bifid median nerve: Normal variant in 15% of population, one trunk may take aberrant course through flexor digitorum superficialis musculature, and often associated with persistent median artery between the two trunks
Important to recognize persistent median artery pre-operatively because could be damaged during surgery
For diagnosis of carpal tunnel syndrome with bifid median nerve: Combined increase of 4 mm2 or more
After carpal tunnel release surgery, median nerve may return to normal diameter or remain enlarged regardless of clinical outcome. Retinaculum may appear thickened or disrupted
Carpal tunnel syndrome can be caused by extrinsic compression by a mass, ganglion cyst, or tenosynovitis

Reference: Klauser AS, Halpern EJ, De Zordo T, et al. Carpal tunnel syndrome assessment with US: value of additional cross-sectional area measurements of the median nerve in patients versus healthy volunteers. Radiology. 2009;250(1):171-177.

To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4

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