CAROTID STENOSIS INDEX - A NEW METHOD OF MEASURING INTERNAL CAROTID-ARTERY STENOSIS

Background and Purpose Current methods of measuring carotid stenosis s uch as those used in the North American Symptomatic Carotid Endarterec tomy Trial (NASCET) and European Carotid Surgery Trial (ECST) have lim itations caused by difficulties in measuring the normal width of the d istal internal carotid artery (ICA) or the carotid bulb. Methods We de veloped a new technique, the Carotid Stenosis Index (CSI), based on th e known anatomic relationship between the common carotid artery (CCA) and ICA (1.2xCCA diameter=proximal ICA diameter). The normal ICA diame ter can therefore be calculated from direct measurement of the CCA. Th ree blinded observers evaluated the angiograms of 57 patients (114 car otid arteries), previously screened with duplex ultrasonography, using the NASCET, ECST, and CSI methods. In a subset of 30 patients undergo ing carotid endarterectomy, comparison was also made to computerized c arotid plaque planimetry. Results The NASCET method could only be appl ied correctly in 89% and the ECST method in 95% of cases because of ov erlying vessels or inadequate views of the distal ICA or carotid bulb. An additional 9% of NASCET cases had a ''negative'' stenosis, in whic h the stenosis is wider than the distal ICA. The CSI method was applic able in 99% of cases. Interobserver comparison using ANOVA revealed si gnificant differences using NASCET (P<.0001) and ECST (P<.001) but not CSI (P=NS). NASCET had a sevenfold variation (P<.01) and ECST a twofo ld variation (P<.01) in results compared with CSI. The intraobserver r eliability was 0.87 for NASCET, 0.86 for ECST, and 0.90 for CSI. Howev er, the 95% confidence intervals for an individual measurement by an o bserver were +/-30% for NASCET, +/-19% for ECST, and +/-15% for CSI. W ith linear methods of measurement there were significant differences b etween NASCET and CSI (P<.0001) and ECST (P<.0001) but not between CSI and ECST. A comparison of area derivations of these methods to caroti d plaque planimetry revealed significant differences from NASCET (P<.0 001) but not ECST, CSI, or duplex methods. A CSI nomogram was created, allowing measurement of both linear and area percent stenosis. Conclu sions CSI is the most reliable validated method of measuring carotid s tenosis, and it correlates with duplex and carotid pathology.