What is the characteristic color Doppler appearance of fibromuscular dysplasia in carotid arteries?

• A. Focal smooth stenosis
• B. Focal aneurysm
• C. String-of-beads with alternating thinning and dilation
• D. Homogeneous color filling with no turbulence

Answer: (C)

Fibromuscular dysplasia produces irregular narrowing with alternating dilated segments along the carotid artery, giving a string-of-beads appearance. This pattern comes from medial fibroplasia causing repeated areas of constriction and dilation, which on color Doppler show multiple narrowings with higher flow velocity and turbulent flow at the transitions, interspersed by dilated sections with lower velocity. It’s distinct from a single smooth stenosis or a lone aneurysm, and it’s not a uniformly filled, turbulence-free lumen.