Angiographic reversed flow ratio as an indicator of high-grade internal carotid stenosis

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.