Overestimation of a stenosis in the internal carotid artery by duplex sonography caused by an increase in volume flow.

PURPOSE: The accuracy of duplex sonography in predicting the degree of an internal carotid artery (ICA) stenosis is decreased when a contralateral high-grade stenosis or occlusion is present. The purpose of this study was to determine whether this overestimation of the stenosis by duplex sonography is associated with an increase in volume flow through the ipsilateral ICA.

METHODS: Forty-seven patients (89 vessels) with a symptomatic ICA stenosis or occlusion who underwent duplex sonography, intraarterial digital subtraction angiography, and magnetic resonance angiography flow quantification of the ICAs were evaluated.

RESULTS: With the use of peak systolic velocity criteria, duplex overestimated stenoses more frequently (chi2: p = 0.03) in vessels with high volume flow (= mean volume flow in control group + 2 SD (>274 ml/min), 46% overestimation) than in vessels with normal or low volume flow (<274 ml/min, 20% overestimation). A correlation coefficient of 0.75 (p < 0.001) was found between volume flow and peak systolic velocity in the distal ICA, indicating that increased volume flow causes the peak systolic velocity to increase. Compared with volume flow in the control group (mean +/- SD = 198 +/- 38 ml/min), volume flow was increased in vessels with a 0% to 49% stenosis (mean +/- SD = 272 +/- 100 ml/min, p < 0.05) and in vessels with a 50% to 69% stenosis (mean +/- SD = 291 +/- 79 ml/min, p < 0.01) when the contralateral ICA had a 70% to 99% stenosis or occlusion.

CONCLUSIONS: Increase in volume flow through the ICA frequently causes overestimation of stenoses in the ICA. Increased volume flow is frequently found in ICAs with a <70% stenosis that are contralateral to ICAs with a >70% stenosis or an occlusion.