Figure 4b. Carpal tunnel syndrome in a 37-year-old man with a persistent median artery of the forearm. (a) Transverse 5-12-MHz gray-scale US scan obtained at the distal radius shows the proximal bifurcation of the median nerve (arrows) and the median artery of the forearm (arrowhead) located between the two nerve branches. (b) Longitudinal color Doppler US scan shows the course of the anomalous artery (arrow) through the carpal tunnel, superficial to the flexor tendons (FT) and deep to the flexor retinaculum (arrowheads). The presence of the artery causes disturbances in nerve function.