Ultrasound assessment of carotid plaques over time

In approximately 15–20% of the cases, stroke results from embolisation arising from atherosclerotic plaques of the carotid bifurcation or of the internal carotid artery [1, 2]. Atherosclerosis is a progressive disease characterised by the accumulation of lipids and fibrous elements in the large arteries [3]. Advanced lesions contain lipid-rich necrotic debris and smooth muscle cells. Fibrous lesions typically have a fibrous cap consisting of smooth muscle cells and extracellular matrix that surrounds and encloses the lipidrich necrotic core. As the plaque progresses, it may exhibit calcifications, ulcerations at the luminal surface and haemorrhage which is presumed to result from small vessels that grow into the lesion from the adventitia of the blood vessel wall [4, 5]. The main mechanism of stroke is thought to be embolism from a fissured or ruptured plaque. Recent pathological studies of postmortem and arterectomy specimens have demonstrated that plaque vulnerability is related to the size of the atheromatous core, the thickness of the fibrous cap and inflammation within the cap. Unstable plaques usually have a thin fibrous cap with a necrotic core situated near the surface. The position of the core and the local thinning of the cap may therefore predispose to rupture which then exposes the thrombogenic atheroma to circulating blood, thus initiating thrombus formation that may lead to thromboembolism and subsequent ischaemic stroke [6, 7]. Duplex ultrasound (DU) is a useful tool for assessment of degree of stenosis and for the characterisation of plaque structure. Degree of stenosis is usually quantified according to three distinct criteria including peak systolic velocities recorded within the jet of the ICA stenosis, the ratio between peak systolic velocities in the ICA and the common carotid artery (CCA) and measurement of stenosis diameter and surface, respectively in a longitudinal and an axial plane [8, 9]. In the longitudinal plane, the measurements may be performed according to NASCET (North American SymptoUltrasound assessment of carotid plaques over time1