Reduced Internal Carotid Artery Flow in Color-coded Carotid Duplex Sonography.

PURPOSE Reduced flow in the internal carotid artery (ICA) is related to cerebral ischemia. We established a classification of reduced ICA flow through color-coded carotid duplex (CCD) sonography. METHODS We retrospectively reviewed 25,000 CCD images in sonography laboratory. RESULTS Reduced ICA flow [flow volume (FV) less than 100 mL/min] was found in 1.2% of all studies, and 270 patients were enrolled. We included 8% patients with lesions proximal to the ICA in Group A, 27% with lesions at the proximal ICA in Group B, 49% with lesions distal to the visible ICA in Group C, and 16% with unknown causes in Group D. Distal ICA stenosis or occlusion is the most common cause of reduced ICA flow. Moyamoya disease, ICA hypoplasia, and ICA dissection were more prevalent in younger patients. CCD of the aforementioned diseases showed similar patterns of upstream high flow resistance with reduced FV in the ICA and were indistinguishable. The collateral flow from bilateral vertebral arteries increased in common carotid artery (CCA) or ICA disease (p less than 0.05) and was exceptionally high in ICA hypoplasia (p less than 0.001). Compared with the FV in the contralateral CCA, that of the ipsilateral CCA decreased in all groups (p less than 0.001), except in patients with low cardiac output. CONCLUSION CCD should be carefully performed and appropriately interpreted in reduced ICA flow. Additional magnetic resonance angiography is helpful in distinguishing stenosis or occlusion from ICA dissection and moyamoya disease, and skull base computed tomography is warranted for the confirmatory diagnosis of ICA hypoplasia. Key Words: color-coded carotid duplex sonography, dissection, hypoplasia, internal carotid artery, reduced flow, stenosis.