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. For example, identification of IPH on MRI in patients with low-grade
carotid artery stenosis is a risk factor for failure of medical
therapy, and studies have shown that such patients may fair better with
carotid endarterectomy (CEA). MR plaque imaging has also been found to be useful in identifying revascularization candidates who would be better candidates for CEA than carotid artery stenting (CAS), as high intraplaque signal on time of flight imaging is associated with vulnerable plaque and increased rates of adverse events in patients undergoing CAS but not CEA.