Atherosclerosis: Pathological Essentials
Atherosclerosis is a chronic inflammatory disease of the arterial intima characterized by the formation of fibro-fatty plaques. It is the primary underlying pathology for ischemic heart disease, stroke, and peripheral artery disease.
1. Pathogenesis: The Response-to-Injury Hypothesis
- Endothelial Injury: Caused by hypertension, hyperlipidemia, smoking, or toxins.
- Lipid Accumulation: LDL accumulates in the intima and undergoes oxidation.
- Monocyte Recruitment: Oxidized LDL attracts monocytes, which differentiate into macrophages and ingest lipid to become foam cells.
- Smooth Muscle Migration: Factors (PDGF) stimulate smooth muscle cell migration from the media to the intima, creating a fibrous cap.
2. Plaque Anatomy & Stability
| Plaque Type | Key Characteristics |
|---|---|
| Stable Plaque | Thick fibrous cap, small lipid core, minimal inflammation. Leads to stable angina. |
| Vulnerable Plaque | Thin fibrous cap, large lipid core, high inflammatory activity (macrophages). Prone to rupture. |
3. Exam Must-Knows
Pathology Pearl: The most important complication is plaque rupture, which exposes highly thrombogenic subendothelial collagen to the blood, triggering the coagulation cascade and acute thrombus formation (MI or stroke).
- Fatty Streaks: The earliest visible lesions, consisting of flat, lipid-laden macrophages. Present even in adolescents.
- Location: Most commonly affects the abdominal aorta (infrarenal), coronary arteries, popliteal arteries, and internal carotid arteries.
- Risk Factors: Hypertension, Hypercholesterolemia (high LDL, low HDL), Smoking, Diabetes Mellitus.