0034: Carotid Interpretation Criteria. How to Choose What You Use

Abstract

The first criteria for estimation of carotid stenosis were developed by the Strandness group at the University of Washington in the 1980s. Others proposed different criteria around the same time. The major carotid surgery trials of the 1990s (NASCET, ECST and ACAS) prompted the development of CDUS criteria to match the 70% and 60% ICA diameter reducing stenosis cut-offs used in these trials. It is to be remembered that these trials used differing methods for estimating stenosis. B mode measurement of stenosis has improved substantially on modern duplex scanners. In 1988 Gray-Weale proposed a classification of carotid plaques on the basis of their echogenicity. Recently interest has returned to plaque characterization with measurement of Gray scale median and other features in an attempt to identify the “vulnerable carotid plaque” and better select asymptomatic patients who might benefit from intervention. The diagnosis of ICA occlusion is important clinically but is not 100% accurate with any of the available imaging modalities. Anatomic information regarding abnormal height of the bifurcation (high or low), the distal extent of the plaque, the diameter of the distal ICA and the presence of tortuosity or kinking of the vessels is also important information and may prompt additional imaging. Care is required in the interpretation of the CDUS and application of standard criteria in a variety of circumstances including contralateral high-grade ICA stenosis or occlusion; elevated CCA velocities and proximal stenosis; tandem ICA stenosis; altered cardiac output states and valvular heart disease, and the presence of intracranial disease. Standard criteria are employed for restenosis follow-up after CEA. Dimensions of the patched bulb should be recorded for serial follow-up. Different criteria with higher cut-off velocities for restenosis and B mode assessment of stent apposition are required following carotid stenting (CAS). A number of consensus panel criteria for carotid stenosis have been developed including the Society of Radiologists in Ultrasound Carotid Stenosis Consensus Conference Criteria (2002) and in Australia, the ASUM criteria (1999). Ideally individual vascular laboratories should validate the criteria they use with the results of alternative imaging modalities and operative pathology. The reality however is that this is increasingly difficult with a reduction in the use of conventional angiography and the dispersion of comparative imaging between CTA, MRA and angiography, each of which has its own inherent limitations for stenosis measurement. This presentation will discuss carotid interpretation criteria with particular emphasis on how the information assists the practicing clinician.