A 68-year-old hypertensive man with poorly controlled dyslipidemia undergoes carotid endarterectomy. The specimen shows a fibrous cap with a necrotic lipid core and evidence of previous plaque hemorrhage. The most important determinant of plaque 'vulnerability' (tendency to rupture) is:

• A Thin fibrous cap (<65 µm) with macrophage infiltration and large lipid core ✓
• B Total plaque volume on imaging
• C Degree of luminal stenosis (>70%) on angiography
• D Calcification of the plaque (calcium score)

Explanation

Plaque vulnerability is primarily determined by the structural integrity of the fibrous cap relative to the hemodynamic forces. A thin fibrous cap (<65 µm by OCT measurement) with heavy macrophage infiltration (macrophages secrete matrix metalloproteinases degrading collagen) overlying a large necrotic lipid core (>40% plaque volume) constitutes the 'thin-cap fibroatheroma' (TCFA), the most vulnerable plaque morphology. Paradoxically, severely stenotic plaques (>70%) are often stable (thick fibrous cap with calcification and dense fibrous tissue), while moderate stenoses harbor more vulnerable soft plaques. This explains why major MIs often occur in previously non-stenotic segments.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.