Detection of total occlusion, string sign, and preocclusive stenosis of the internal carotid artery by color-flow duplex scanning

Background: Stroke prevention depends on the accurate differentiation of surgically treatable preocclusive lesions from total occlusions of the internal carotid artery. This prospective study was undertaken to review the accuracy of color-flow duplex scanning for identifying carotid string signs, focal preocclusive lesions (95% to 99% stenoses), and total occlusion of the internal carotid artery. Materials and methods: Over an 18-month period, 4,362 patients underwent color-flow duplex scanning of the carotid arteries. Angiograms of 596 internal carotid arteries were available for comparison with the duplex scan findings. Total occlusion was diagnosed by the absence of flow in internal carotid arteries visualized on B-mode scanning. Preocclusive lesions were identified by a trickle of flow in the vessel lumen. Results: Of 65 color-flow duplex scans that predicted total occlusion, 64 (98%) were confirmed by angiography. The negative predictive value for total occlusion was 99%. Twenty-six (87%) of 30 string signs and focal 95% to 99% stenoses were correctly identified. Color-flow scanning prediction of preocclusive lesions was accurate in 84% of 31 cases. Low velocities in the internal carotid artery were usually associated with a string sign, and high velocities with a focal preocclusive lesion. Conclusions: Color-flow duplex scanning accurately differentiates between stenotic and totally occluded internal carotid arteries. Identification of preocclusive lesions is not as accurate but the results are promising. Arteriographic confirmation of duplex scan findings is necessary only when scans are equivocal.