The influence of contralateral carotid stenosis on duplex accuracy: The role of collateral cerebral flow

Duplex ultrasonographic (DU) overestimation of internal carotid artery (ICA) stenosis contralateral to high-grade ipsilateral stenosis has been previously reported. The current study was undertaken to evaluate the incidence of and factors contributing to these DU errors, which can adversely affect DU accuracy. Fifty-six patients undergoing carotid endarterectomy (CEA) with unilateral stenosis of ≥50% and a patent contralateral ICA (CICA) were evaluated preoperatively by DU and angiography. Severity of ICA stenosis and the presence of intracranial crossfilling was determined by angiography. The mean stenosis in arteries undergoing CEA was 83% and intracranial collateralization was observed in 27 patients. Seventeen cases of duplex/angiogram divergence resulted in overestimation of CICA narrowing. CICA duplex/angiographic divergence was not observed to be related to age, sex, symptomatology, diabetes mellitus, hypertension, crossfilling, or degree of ipsilateral stenosis. Intracranial crossfilling was related to increasing ipsilateral stenosis but not influenced by the above factors. Six weeks postoperative 8 of the 17 (47%) spurious duplex findings reconciled with angiography followed by an additional 4 at 1 year. Crossfilling was not observed more frequently in the 12 patients in whom spurious results later reconciled. The results of this study suggest that overestimation of CICA stenosis is unpredictable. Although relief of carotid obstruction did affect subsequent CICA duplex findings, suggesting a hemodynamic explanation for this phenomenon, the results did not support a relationship to crossfilling.