Contemporary carotid imaging: from degree of stenosis to plaque vulnerability

Abstract

abbreviatioNs AHA = American Heart Association; CAS = carotid artery stenting; CEA = carotid endarterectomy; CEUS = contrast-enhanced ultrasonography; CTA = CT angiography; DCE = dynamic contrast-enhanced; DSCT = dual-source CT; FDG = fluorodeoxyglucose; FSE = fast spin echo; Gd = gadolinium; HU = Hounsfield units; IPH = intraplaque hemorrhage; LRNC = lipid-rich necrotic core; MDCT = multidetector-row CT; MDCTA = MDCT angiography; MES = microembolic signal; MMP-9 = matrix metalloproteinase-9; MRA = MR angiography; PDW = proton density-weighted; SUV = standardized uptake value; SUVmax = maximal SUV; TBR = target-to-background ratio; TCD = transcranial Doppler ultrasonography; TIA = transient ischemic attack; TOF = time of flight; USPIO = ultrasmall superparamagnetic iron oxide. Carotid artery stenosis is a well-established risk factor of ischemic stroke, contributing to up to 10%-20% of strokes or transient ischemic attacks. Many clinical trials over the last 20 years have used measurements of carotid artery stenosis as a means to risk stratify patients. However, with improvements in vascular imaging techniques such as CT angiography and MR angiography, ultrasonography, and PET/CT, it is now possible to risk stratify patients, not just on the degree of carotid artery stenosis but also on how vulnerable the plaque is to rupture, resulting in ischemic stroke. These imaging techniques are ushering in an emerging paradigm shift that allows for risk stratifications based on the presence of imaging features such as intraplaque hemorrhage (IPH), plaque ulceration, plaque neovascularity, fibrous cap thickness, and presence of a lipid-rich necrotic core (LRNC). It is important for the neurosurgeon to be aware of these new imaging techniques that allow for improved patient risk stratification and outcomes. For example, a patient with a low-grade stenosis but an ulcerated plaque may benefit more from a revascularization procedure than a patient with a stable 70% asymptomatic stenosis with a thick fibrous cap. This review summarizes the current state-of-the-art advances in carotid plaque imaging. Currently, MRI is the gold standard in carotid plaque imaging, with its high resolution and high sensitivity for identifying IPH, ulceration, LRNC, and inflammation. However, MRI is limited due to time constraints. CT also allows for high-resolution imaging and can accurately detect ulceration and calcification, but cannot reliably differentiate LRNC from IPH. PET/CT is an effective technique to identify active inflammation within the plaque, but it does not allow for assessment of anatomy, ulceration, IPH, or LRNC. Ultrasonography, with the aid of contrast enhancement, is a cost-effective technique to assess plaque morphology and characteristics, but it is limited in sensitivity and specificity for detecting LRNC, plaque hemorrhage, and ulceration compared with MRI. Also summarized is how these advanced imaging techniques are being used in clinical practice to risk stratify patients with low- and high-grade carotid artery stenosis....

Thirty‐day recurrence after ischemic stroke or TIA

“…TOAST criteria require an intra‐ or extracranial stenosis of >50% to classify a stroke as LAA, a criterion originating from the NASCET study in which carotid stenoses were graded from angiograms (North American Symptomatic Carotid Endarterectomy Trial Collaborators et al, 1991). Since then, growing evidence shows that even in nonstenotic intra‐ or extracranial arteries, high‐risk atherosclerotic plaques may be the culprit of IS or TIA due to artery‐to‐artery embolization (Brinjikji et al, 2016; Kim & Kim, 2014). These cases nevertheless often end up being classified as cryptogenic, which may explain why patients with LAA in our study were initially classified as SUE, as more modern imaging techniques like emboli detection monitoring and contrast‐enhanced ultrasound were not routine practice in our stroke unit in the study period.…”

Imaging of the ulcerated carotid atherosclerotic plaque: a review of the literature

“…MRI’s particular strength in detection of ulcerations relies on its ability to image the plaque’s fibrous cap as a black zone lying between the bright lumen and the grey plaque content. Absence of this dark zone represents rupture of the fibrous cap and thus ulceration [111, 112]. If blood pool agents were used, then CE-MRA was found superior to MDCTA both for grading of stenosis and characterisation of plaque morphology [113].…”

Recent Trends in Neuro-endovascular Treatment for Acute Ischemic Stroke, Cerebral Aneurysms, Carotid Stenosis, and Brain Arteriovenous Malformations

“…Furthermore, improved imaging techniques such as CT, magnetic resonance imaging, and ultrasonography have enabled us to understand not only the degree of carotid artery stenosis but also the vulnerability of the plaque, which stratify the risk of patients or treatments. 36) …”