OVERESTIMATION OF A STENOSIS IN THE INTERNAL CAROTID-ARTERY BY DUPLEXSONOGRAPHY 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 contral ateral high-grade stenosis or occlusion is present. The purpose of thi s study was to determine whether this overestimation of the stenosis b y duplex sonography is associated with an increase in volume now throu gh the ipsilateral ICA. Methods: Forty-seven patients (89 vessels) wit h a symptomatic ICA stenosis or occlusion who underwent duplex sonogra phy, intraarterial digital subtraction angiography, and magnetic reson ance angiography flow quantification of the ICAs were evaluated. Resul ts: With the use of peak systolic velocity criteria, duplex overestima ted stenoses more frequently (chi(2) : p = 0.03) in vessels with high volume now (= mean volume now in control group + 2 SD (>274 ml/min), 4 6% overestimation) than in vessels with normal or low volume flow (<27 4 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 sys tolic velocity to increase. Compared with volume flow in the control g roup (mean +/- SD = 198 +/- 38 ml/min), volume flow was increased in v essels 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% st enosis or occlusion. Conclusions: Increase in volume now through the I CA 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.