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An international consensus meeting to determine criteria for the characterization of extracranial carotid artery stenosis was held in Paris on December 13–14, 1996. Recommendations are the following if the degree of the stenosis and the precise location of the stenosis are well defined. Ultrasonic Doppler duplex methods describe the composition and the surface topography of carotid plaques. Echogenicity (from anechoic to hyperechoic), surface (from smooth to cavitated) and texture (from homogeneous to heterogeneous) are the features to be estimated as plaque thickness and length. Echogenicity is standardized against blood (anechoic), mastoid muscle (isoechogenic) or bone (hyperechogenic cervical vertebrae). Luminal surface is classified into three classes: regular, irregular (0.4–2 mm depth) and ulcerated (>2 mm depth with a well-defined back wall at its base and a color Doppler injection). Texture is a function of pixle size and, in a given region of interest, reflects the variability of the grey scale values. Recommended technical requirements are frequency- and amplitude-modulated color Doppler flow imaging, carrier frequency >5 MHz capable of insonating up to 4 cm and retrievable documentation of relevant findings. Computed tomographic angiography permits three-dimensional rendering of the size and extent of the plaque and allows to recognize calcifications, deposits, plaque isodense to muscle and ulcers >2 mm in size. Angiography may identify gross calcifications and large ulcers defined in two classes: 1 – large (2 mm depth by 2 mm width) and 2 – complex with multiple craters. Magnetic resonance imaging with or without angiography may play a role in the future. In vitro studies show that MR can demonstrate plaque components such as fibrosis, calcification, hemorrhage and necrotic core, but current technical limitations related to resolution and motion artifacts prevent this from being implemented in vivo. Pathological studies require en bloc surgery. Component areas should be calculated from their length and width, and ulcerations measured from their width. The risk of cerebrovascular ischemia is clearly related to the degree of stenosis. Factors of individual importance for higher risk include in descending importance: evidence of progression, surface ulceration and low echogenicity. Texture is still under investigation as a prognostic factor.

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