A Plaque Instability Index Calculated by Histological Marker Analysis of the Endarterectomy Carotid Artery

(1) Background: Atherosclerosis is a pandemic condition that causes the development of ischemic syndromes including myocardial infarctions and many strokes, in addition to disabling peripheral artery disease. Progression of atheroma plaques has been associated with an increased risk of mortality. It is a challenge to determine in advance if atherosclerotic plaque will become unstable by calculating an index of instability. We proposed a score of ten parameters for the assessment of high-risk plaques, by quantification of 10 risk factors for acute cardiovascular events, most of them representing histological variables. (2) Methods: Carotid endarterectomy samples were collected from 10 highly symptomatic patients who matched for gender, age, risk factors, and plaque morphology. Samples were stained with hematoxylin-eosin, elastic van Gieson, Perls, and Mallory. Immunohistochemistry was performed using specific antibodies, such as CD31 for endothelial cells, CD68 for macrophages, and CD3 for T cells. (3) Results: For each plaque, the presence and/or number of histological features (fibrous cap thickness, lipid core size, plaque and cap infiltration with macrophages and lymphocytes, neovessels, intraplaque hemorrhage, parietal thrombi, and calcium deposits) were recorded on a simple semi-quantitative one- or two-grade scale. The study identified four stable plaques (SPs), two vulnerable plaques (VPs), and four unstable plaques (USPs). We found significantly more macrophages and neovessels in unstable plaques compared with stable plaques. The score for unstable plaques was higher than that for VP. (4) Conclusions: The study showed that symptomatic carotid disease is associated with an increased index score. The proposed algorithm for carotid plaque assessment may be useful for an imaging application.