Ultrasonographic assessment of the morphological characteristics of the carotid plaque

Apart from the degree of stenosis, plaque morphology has emerged in recent years as an important contributory factor in stroke risk. Ultrasound studies have shown that hypo- or anechogenic plaques carry a higher risk of cerebrovascular events than echogenic ones. Similarly, heterogeneous plaques presenting a complex pattern of echogenicity in ultrasound have also been more frequently associated with the occurrence of neurological symptoms than homogeneous lesions. Further, most studies determining the surface characteristics in ultrasound have found that ulceration also predicted increased risk of subsequent stroke. These studies are, however, based on visual evaluation using different classification systems and presenting a high variability of intra- and interobserver agreement. A quantitative method using a computerised image analysis of the plaque based on a grey-scale median (GSM) value has recently been developed which allows a more objective and reproducible evaluation of plaque echogenicity. Several studies have also shown that low GSM values are associated with an increased stroke incidence. A stratified GSM analysis determining the GSM in each one millimeter-thick stratum of the plaque may represent an additional method of determining different components of unstable plaques, such as thinning of the fibrous cap and the position of the necrotic core near the surface. This article reviews the ultrasonic morphology of the carotid plaque, its clinical prognostic value and correlations with histopathological studies. Recent ultrasound developments in the assessment of plaque echogenicity are also discussed.