Symptomatic Mild Carotid Artery Stenosis

predict the risk of future ischemic events in patients with carotid artery stenosis based on ultrasound findings that assessed morphology and composition of plaque. However, with publication of landmark clinical trials, leading to a definition of the indications for treatment of symptomatic and asymptomatic patients, the focus was exclusively on the degree of stenosis rather than plaque morphology and composition. Therefore, over the past 30 years, decisions for invasive treatment have been based on degree of stenosis, and this is reflected in published guidelines. However, a growing body of scientific evidence suggests that a culprit plaque is not necessarily large and causing “clinically significant stenosis,” but vulnerable (ie, prone to rupture or to develop ulcers and erosions) and thrombogenic—leading to sudden occlusion, emboli, and subclinical microemboli with the potential to recur over time. The bulk of this research, which was mostly in the coronary arteries, has led to a broad awareness in the cardiology community of the importance of plaque morphology and composition, in addition to the degree of stenosis, in influencing the risk of future ischemic events. The concept of “unstable” plaque, independent from the degree of stenosis, has been the basis for intensive research in high-resolution intravascular imaging platforms and aggressive therapeutic measures. More recently, advances in noninvasive imaging that improved visualization of plaque features such as hemorrhage, and a better understanding of the mechanism leading to thromboembolic events, have raised awareness within the stroke community about the concept of “vulnerable carotid plaque.” This has led to the identification of patients with mildly stenotic but vulnerable plaque and whose cases would otherwise have been diagnosed as strokes of “undetermined source.” In this article, we briefly summarize pathologic, imaging, and clinical criteria of unstable plaque in patients with mild carotid artery stenosis, with case examples.