Angiographic Reversed Flow Ratio as an Indicator of High-Grade Internal Carotid Stenosis

Abstract

Purpose To examine differential flow through internal carotid artery (ICA) and external carotid artery (ECA) circulations on digital subtraction angiography (DSA) as an indicator of carotid stenosis. Materials and Methods Carotid and cerebral angiograms ( N = 148) were retrospectively evaluated, with flow through ICA and ECA circulations scored on a five-point flow scale ratio: a score of 1 indicated ICA flow arrived at the vertex at least 1 second before ECA flow, a score of 3 indicated ICA and ECA flow arrived at the same time, and a score of 5 indicated ECA flow reached the vertex at least 1 second before ICA flow. Sensitivities and specificities for ICA stenosis detection were determined for flow ratios. Results Sensitivity and specificity varied with stenosis severity and flow grade. In general, deranged flow was an insensitive marker for stenosis; however, flow ratio equalization or frank ratio reversal was a highly specific indicator of ICA stenosis. A flow grade of 3–5 was 88% specific (95% CI, 79%–94%) and 66% sensitive (95% CI, 53%–77%) for stenosis of 70% or greater. A grade of 4 or 5 was 99% specific (95% CI, 93%–99%) and 24% sensitive (95% CI, 15%–37%) and a grade of 5 was 100% specific (95% CI, 94%–100%) and 18% sensitive (95% CI, 9%–29%) for carotid stenosis of 70% or greater. Conclusions Identification of deranged differential flow between the ICA and ECA circulations is an insensitive but highly specific marker for high-grade stenosis. Therefore, if flow reversal is identified but the apparent carotid stenosis is mild, further angiographic projections should be used to uncover a highly probable severe carotid stenosis.