A 62-year-old woman with a 20-year history of smoking, hypertension, and hyperlipidemia (LDL 180 mg/dL) undergoes coronary angiography for stable angina. The angiogram reveals a 60% stenosis of the left anterior descending artery with a smooth, concentric appearance and no thrombus. Intravascular ultrasound (IVUS) shows a plaque with predominantly smooth muscle cells, collagen-rich fibrous tissue, and minimal lipid content. Histopathological examination of a similar lesion from another patient shows organized layers of smooth muscle cells in a collagen matrix with a thick, intact fibrous cap. Which of the following best describes the stage of atherosclerotic plaque development in this patient?

Explanation

## Stages of Atherosclerotic Plaque Development ### Classification of Atherosclerotic Lesions The American Heart Association (AHA) classifies atherosclerotic plaques into six morphological stages, progressing from early fatty streaks to complicated plaques with thrombosis. | Stage | Histology | Clinical Significance | Angiographic Appearance | |-------|-----------|----------------------|------------------------| | **Type I (Fatty Streak)** | Macrophages + foam cells, minimal smooth muscle | Reversible; no hemodynamic effect | Not visible | | **Type II (Intermediate)** | Smooth muscle proliferation begins; small lipid pools | Transitional phase | Not visible | | **Type III (Fibrous Plaque)** | Smooth muscle cells + collagen; lipid core present | **Hemodynamically significant; stable** | **Concentric, smooth stenosis** | | **Type IV (Core Plaque)** | Large lipid necrotic core; thin cap | Vulnerable; prone to rupture | Eccentric, irregular | | **Type V (Fibrocalcific)** | Calcification + collagen; variable lipid | Stabilized but rigid | Dense, calcified appearance | | **Type VI (Complicated)** | Plaque rupture, thrombus, hemorrhage | Acute coronary syndrome | Thrombus, irregular borders | **Key Point:** The patient's presentation—**stable angina, smooth concentric stenosis on angiography, IVUS showing smooth muscle cells and collagen with minimal lipid, and intact fibrous cap**—is diagnostic of **Type III (Fibrous Plaque)**. ### Pathological Features of Fibrous Plaque (Type III) 1. **Smooth muscle cell proliferation** — dominant cell type 2. **Collagen deposition** — organized, cross-linked extracellular matrix 3. **Thick, intact fibrous cap** — provides mechanical stability 4. **Small lipid pools** — present but not dominant 5. **Minimal macrophage infiltration** — low inflammatory activity 6. **Hemodynamically significant** — 50–70% stenosis typical **High-Yield:** Fibrous plaques are **stable** and produce **chronic, predictable symptoms** (stable angina). They do NOT rupture acutely because the fibrous cap is thick and well-organized. This contrasts with thin-cap fibroatheromas, which are vulnerable to rupture. ### Clinical Pearl: Why This Patient Has Stable Angina The smooth, concentric morphology and organized collagen-rich structure indicate a mature, stable plaque that narrows the lumen gradually. The intact fibrous cap prevents thrombosis. Symptoms occur only when the stenosis exceeds the coronary reserve (typically >70% diameter stenosis at rest, or >50% with stress). **Mnemonic:** **SCAM** = **S**mooth muscle + **C**ollagen + **A**rteriosclerotic + **M**ature plaque = stable fibrous lesion. [cite:Robbins 10e Ch 11]