Accuracy of duplex scanning in the detection of stenosis after carotid endarterectomy

The results of duplex ultrasonography in grading stenosis after carotid endarterectomy (78 sites) were compared with those of contrast angiography in 71 patients studied for recurrent or contralateral occlusive disease of the carotid bifurcation. Duplex and angiographic studies were performed within one month of each other at a mean postoperative interval of 44 months (range 3 to 122 months). Stenosis of the common carotid (CCA) and internal carotid artery (ICA) was classified into five disease categories (normal or less than 15% diameter reduction [DR], 16% to 49% DR, 50% to 75% DR, greater than 75% DR, and occlusion). The overall accuracy of duplex scanning compared with angiography in predicting recurrent carotid bifurcation disease was 83%, a level of agreement similar to classification of disease involving the nonoperated, contralateral bifurcation (overall accuracy 87%). Recurrent stenosis (greater than 50% DR) or occlusion of the CCA or ICA after endarterectomy was identified with an accuracy of 97%. Overestimation of severity of recurrent stenosis accounted for 11 of 13 duplex classification errors (85%). Presence of moderate (30% to 50% DR) recurrent stenosis of the CCA, tortuosity of the ICA, and severe contralateral carotid bifurcation disease were associated with velocity spectra that predicted a more severe recurrent stenosis at the endarterectomy site compared with angiographic grading. The level of agreement between duplex scanning and angiography was comparable to the interobserver variability in angiographic interpretation. The accuracy reported justifies the use of duplex scanning to grade the severity of carotid bifurcation recurrent stenosis and to follow these lesions for disease progression.