The inaccuracy of simple visual interpretation for measurement of carotid stenosis by arteriography

Purpose: To determine intraobserver and interobserver variability of carotid arteriography interpretation as well as the reliability of simple visual interpretation (SVI) or "eyeballing" of arteriography in the measurement of internal carotid artery stenoses. Methods: Intraobserver and interobserver measurements of 200 carotid arteriograms were performed in a blinded fashion by two vascular surgeons (VS1 and VS2) using a digital caliber computer program similar to software available in catheterization laboratories. The distal normal internal carotid artery was used as a frame of reference. These computer-derived measurements were compared with previous SVI measurements, found by retrospective chart review, that were performed at the initial time of arteriography. Results: Intraobserver agreement (VS1a vs VS1b and VS2a vs VS2b) within ±5% using the computer program was 94% and 92%. Interobserver agreement within ±5% using the computer program for the four possible combinations ranged from 43% to 48%. Interobserver agreement using the computer program increased to 83% to 88% for correct stenosis interpretation within ±20%. In the 16% to 49% category (by computer measurement), SVI would have placed the stenosis in a higher category 40% to 56% of the time. Likewise, in the 50% to 79% category, comparing SVI with the four different computer caliber measurements, SVI overestimated the stenosis to the 80% to 99% category by 30% to 44%. In the 80% to 99% category, SVI overestimated lesions in 27% to 51% of the cases. All occlusions seen on SVI correlated with computer program measurements. The computer readings in many cases downgraded the degree of carotid stenosis into a lower category and in some cases, may have led to a different treatment paradigm. SVI never underestimated carotid stenosis compared with all matched computer program measurements. Conclusions: Compared with a method of objective measurement similar to that used in a catheterization laboratory, SVI overestimated most carotid artery stenoses. Given the coming era of carotid stenting and a renewed need for arteriography before carotid intervention, knowledge of variability and correct interpretation of carotid stenosis using available technology remains paramount to warranted treatment.