References for this Review were identified through searches of PubMed with the search terms “carotid artery”, “atherosclerotic plaque”, “stroke”, “computed tomography”, “ultrasound”, “magnetic resonance imaging”, and “digital subtraction angiography” from January, 1980, to January, 2009. Only papers published in English were reviewed in detail. The final reference list was selected on the basis of relevance to the topics covered in this Review.
ReviewCarotid-artery imaging in the diagnosis and management of patients at risk of stroke
Introduction
Stroke is the second most common cause of death in developed countries, causing 4·5 million deaths every year.1 Stroke is also a major source of morbidity and long-term disability, resulting in substantial economic burden on health and social services worldwide. Despite advances in medical therapies and thrombolysis, effective stroke treatment remains elusive, in general terms, for various practical reasons. Therefore, prevention of stroke is still a paramount issue.
Up to 15% of cerebral infarctions are estimated to be associated with embolic debris and thrombi originating from atherosclerotic plaques at the carotid bifurcation.2 The risk of stroke in patients with carotid atherosclerosis is closely associated with the severity of luminal stenosis. For asymptomatic patients with less than 75% stenosis, the yearly risk of stroke is less than 1%, but this risk increases to 2–5% for patients with stenosis greater than 75%.3, 4, 5 The risk is much higher in symptomatic patients (ie, those who have had previous transient ischaemic attacks or strokes) at 10% in the first year for those with severe lesions, with risk rising to 30–35% over the next 5 years.6 There is much clinical interest in carotid atherosclerotic disease because it is one of the major potentially preventable causes of stroke. Three pivotal studies (NASCET [the North American Symptomatic Carotid Endarterectomy Trial], ECST [the European Carotid Surgery Trial], and the Veteran Affairs Cooperative Studies Program Trial) have clearly shown the benefits of carotid endarterectomy compared with medical treatment in recently symptomatic patients with severe carotid stenosis.7, 8, 9 The pooled analysis of these three trials showed significant benefits of surgery in the group with severe stenosis (70–99% stenosis in NASCET; absolute risk reduction of 16%, p<0·001) after 5 years of follow-up.10 This finding equates to a net prevention of about one stroke after operating on six patients with severe carotid stenosis.10 In patients with mild stenosis (50% or less in NASCET), the risks incurred during carotid endarterectomy outweighed the benefits of surgery.10 Patients with moderate stenosis (50–69% in NASCET) still benefited from surgery, although the overall gains were more modest than in patients with severe stenosis, with an absolute risk reduction of 4·6% after 5 years.10 With improvements in technology such as distal protection devices and low-profile self-expanding stents, carotid angioplasty and stenting has emerged as a viable alternative to carotid endarterectomy. However, the role of stenting outside clinical trials remains uncertain and is, at present, recommended only in patients at high risk for surgical complications.11
In asymptomatic carotid-artery disease, the efficacy of carotid endarterectomy is also poorly defined. Although several groups have reported no benefits from surgery,12, 13, 14 results from ACAS (Asymptomatic Carotid Atherosclerosis Study) showed that surgery for patients with stenosis greater than 60% resulted in a 5-year ipsilateral stroke rate of 11%, whereas optimum medical treatment (daily aspirin and medical risk factor management) resulted in a stroke rate of 5·1%.15, 16 The UK Medical Research Council ACST (Asymptomatic Carotid Surgery Trial) Collaborative Group confirmed a modest benefit of carotid endarterectomy in asymptomatic patients who were younger than 75 years and who had at least 70% carotid stenosis on ultrasound: immediate carotid endarterectomy halved the net 5-year stroke risk from about 12% to about 6%.17 Despite the modest benefit, there is an increasing trend to operate on asymptomatic patients, both in North America and Europe.18
There is a growing body of evidence from observational and epidemiological studies that the risk of subsequent stroke in patients with carotid stenosis is highest in the first few weeks after onset of transient ischaemic attacks or minor strokes, and this risk declines rapidly thereafter.19, 20, 21 This finding implies a short time window for effective stroke prevention, necessitating the rapid identification of patients with substantial carotid stenosis and the swift initiation of medical treatment or revascularisation procedures. The mainstay of carotid imaging is, therefore, not only to enable accurate grading of the severity of stenosis, but also to facilitate delivery of treatment within this short time window.
In this Review, we discuss current state-of-the-art non-invasive diagnostic imaging strategies for luminal stenosis. We also briefly describe novel and promising plaque imaging techniques that can be used to characterise vulnerable carotid-plaque features in vivo and can provide additional information to that obtained with luminal stenosis alone.
Section snippets
Digital subtraction angiography
Digital subtraction angiography (DSA), as used in NASCET and ECST, is still considered to be the most accurate method for assessment of carotid stenosis.7, 8 DSA is an invasive technique that requires femoral-artery puncture and direct intra-arterial injection of contrast medium, usually in the common carotid arteries. High-resolution images of the stenotic lumen can be obtained, as well as estimation of flow dynamics, such as slow and delayed blood flow (figure 1). Intracranial views are
Doppler ultrasound
Doppler ultrasound is well established as an accurate, non-invasive method to assess carotid stenosis. This technique is inexpensive and portable, and provides reliable information on the localisation and extent of stenosis, flow dynamics, plaque structure, and vessel-wall characteristics. Several studies have shown the accuracy of this technique,40, 45 but have also indicated its limitations: high operator variability,46 inter-hospital variability,47 susceptibility to artefacts from calcified
Trends and controversies in non-invasive imaging
Although there were already many published studies dealing with non-invasive carotid imaging at the start of the 21st century, there was much controversy, even among experts, on whether non-invasive tests were accurate enough to replace DSA.76, 77 Some authors argued that non-invasive tests were not safer than DSA if substantial misclassification of stenosis resulted in inappropriate selection of patients for surgery. Part of the problem was that many of the available studies were undermined by
Carotid-plaque imaging
The benefits of carotid endarterectomy in recently symptomatic patients with severe carotid stenosis are well established. However, there are subgroups of patients, particularly those with moderate stenosis or who are asymptomatic, in whom the choice between revascularisation or medical intervention is less clear and for whom better methods of risk stratification are needed.93 This has led many investigators to research other factors associated with carotid plaques that might be markers of
Conclusions
Non-invasive techniques have mostly superseded DSA in the routine assessment of carotid stenosis. These techniques are more readily accessible than DSA and their accuracy, although lower, is now considered to be sufficient to outweigh the risks associated with DSA. Among the non-invasive diagnostic strategies, a combination of screening with Doppler ultrasound and confirmatory MRA or CT angiography is currently favoured by many centres, with some still advocating DSA in cases in which there is
Search strategy and selection criteria
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2022, Journal of Stroke and Cerebrovascular DiseasesCitation Excerpt :However, for low-grade stenosis (< 50%), the apparent benefit of carotid endarterectomy (CEA) and the greater risk of cerebral infarction than the risk of complication of CEA have not been established. Recent vascular biology studies indicate that plaque vulnerability is an important risk factor of ischemic events.3,4 Therefore, many investigations have evaluated plaque characteristics by magnetic resonance imaging (MRI).5–7
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2018, PhotoacousticsCitation Excerpt :Biomedical imaging of the carotid artery is therefore of primary importance for determining disease risk, preparing for surgical intervention, and monitoring treatment outcomes. Favorable characteristics of carotid imaging include accurate, high resolution, repeatable, and operator-independent capabilities that facilitate diagnosis and treatment in a rapid time window with minimal risk [2]. Furthermore, imaging that is practical for screening and allows for longitudinal studies to better understand cardiovascular disease is desirable [6].