Presentation
Tingling and numbness of the right hand
Patient Data
The right median nerve in the carpal tunnel is flattened with a hypoechoic echopattern and an indistinct fascicular pattern. Its surface area measures about 29 mm2 (the maximum suggested surface area is about 12 mm2). The short axis of the nerve measures 3.3 mm, while its long axis measures 10.4 mm. The flattening ratio = 3.15 (a flattening ratio> 3 suggests carpal tunnel syndrome). The nerve surface area is 6 mm2 in the forearm. Dynamic study shows the sliding movement of the nerve to the top of the carpal tunnel and its compression by the flexor retinaculum (which appears ventrally bowed). The left side was used for comparison, which revealed a median nerve surface area measuring 9 mm2 and 11 mm2 in the forearm and the carpal tunnel respectively.
Annotated image of the contents and boundaries of the carpal tunnel:
flexor digitorum superficialis tendons (white arrowhead)
flexor digitorum profundus tendons (green arrowhead)
the flexor retinaculum (light blue arrow)
the shadow exerted by the scaphoid (blue arrow)
the shadow exerted by the pisiform (red arrow)
Case Discussion
Carpal tunnel syndrome is the most common entrapment neuropathy of the peripheral nerves. Sonographic signs suggestive of carpal tunnel syndrome include hypoechoic echopattern of the median nerve, flattening of the ventral surface of the nerve, discrepancy of more than 2 mm between the nerve surface area in the distal forearm and the proximal carpal tunnel and median nerve surface area greater than 10 mm2 (for single nerve trunk) and 12 mm2 (for bifid median nerve).
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