Carpal tunnel syndrome - ultrasound
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Findings suggestive of carpal tunnel syndrome on the right with distortion and flattening of the median nerve.
- enlargement of the nerve proximal to the flexor retinaculum (compared to contralateral asymptomatic side)
- distal flattening of the nerve (seen on transverse image)
- palmar bowing of the flexor retinaculum (>2 mm beyond a line connecting the pisiform and the scaphoid)
Enlargement of the nerve distal to the flexor retinaculum seems to be the most sensitive and specific criterion, but what cut-off value for pathological size remains debated; normal cross-sectional area is given at 9-11 mm², but the range of sizes deemed pathological is wide.