Identifying the carotid 'high risk' plaque: is it still a riddle wrapped up in an enigma?

The selection of patients for many vascular interventions has largely been based on the severity of luminal narrowing. However, histological data from the coronary and carotid circulations suggest that other plaque features such as inflammation and fibrous cap thickness may be more important in predicting future thrombo-embolic events. This paper reviews the available evidence for identifying carotid atheroma at high risk of being associated with clinical events. Despite a large number of imaging and biomarker studies, 'presenting symptoms' remains the most clearly identified risk predictor for ischaemic stroke in patients with carotid stenosis. At present, no imaging modality or plasma biomarker has clearly identified a high risk sub-group of asymptomatic carotid stenoses for which the benefit of carotid intervention is comparable to that of symptomatic atherosclerosis. Emerging developments in MRI, transcranial Doppler and scintigraphic imaging hold some promise for the future. However, the multiple mechanisms and sites determining ischaemic stroke occurrence in association with atherosclerosis suggests that systemic therapies are likely to be the most powerful modality in the management of asymptomatic disease.