A 52-year-old woman from Mumbai with a 10-year history of poorly controlled hypertension (BP 180/110 mmHg) and hyperlipidemia presents with progressive exertional chest pain for 3 months. She denies smoking and diabetes. Coronary angiography reveals a 70% stenosis of the left anterior descending artery with a smooth, calcified lesion. Intravascular ultrasound (IVUS) shows a thick fibrous cap (>200 μm) with minimal lipid content and extensive calcification. Histopathology of a biopsy specimen shows smooth muscle cells with abundant collagen, sparse macrophages, and calcified deposits. The lesion is successfully treated with percutaneous coronary intervention and stent placement. Which of the following best describes the pathological nature of this atherosclerotic lesion?

Explanation

## Pathological Classification of Atherosclerotic Lesions ### Stable vs. Vulnerable Plaques: Key Distinctions | Feature | Stable Plaque | Vulnerable Plaque | |---------|---------------|-------------------| | **Fibrous cap thickness** | Thick (>200 μm) | Thin (<65 μm) | | **Lipid core size** | Small or minimal | Large, lipid-rich | | **Calcification** | Extensive, dense | Sparse or absent | | **Smooth muscle cells** | Abundant, active | Few, apoptotic | | **Macrophage infiltration** | Sparse | Dense | | **Collagen content** | Abundant, organized | Disorganized | | **Risk of rupture** | Very low | Very high | | **Clinical presentation** | Stable angina, chronic stenosis | Acute MI, unstable angina | | **Angiographic appearance** | Smooth, eccentric or concentric | Irregular, ulcerated | ### Pathological Features in This Case **Key Point:** This patient has a **stable, fibrocalcific atherosclerotic plaque** characterized by: - **Thick fibrous cap (>200 μm)**: Protective against rupture; composed of smooth muscle cells and collagen. - **Minimal lipid content**: Low thrombogenic potential. - **Extensive calcification**: Hallmark of chronic, remodeled lesions; indicates plaque maturation and stabilization. - **Sparse macrophages**: Low inflammatory activity; suggests chronic, quiescent lesion. - **Abundant collagen and smooth muscle cells**: Indicate fibrotic remodeling and plaque stabilization. ### Mechanisms of Chronic Obstruction **High-Yield:** Stable plaques cause symptoms through **mechanical stenosis**, not thrombosis: 1. **Positive remodeling phase**: Initial outward expansion of the vessel wall accommodates plaque growth without luminal narrowing. 2. **Constrictive remodeling phase**: As plaque accumulates and fibroses, the vessel wall cannot expand further; the plaque encroaches on the lumen. 3. **Progressive stenosis**: Over months to years, the lesion narrows the arterial lumen, reducing blood flow and causing exertional angina. 4. **Calcification**: Calcium deposition stabilizes the plaque, reducing rupture risk but increasing lesion rigidity. **Clinical Pearl:** The 70% stenosis with smooth, calcified appearance on angiography and the 3-month progressive course are consistent with **chronic hemodynamic obstruction** from a stable plaque, not acute thrombotic occlusion. ### Why This Patient's Presentation Differs from Acute Coronary Syndrome **Key Point:** This patient presents with: - **Stable exertional angina** (predictable, reproducible, relieved by rest)—not acute chest pain. - **Chronic stenosis** (70% narrowing)—not acute occlusion. - **Smooth, calcified lesion** on angiography—not irregular or ulcerated. - **Thick fibrous cap** on IVUS—not thin or ruptured. These features exclude acute thrombotic mechanisms and point to chronic hemodynamic obstruction. ### Clinical Management Implications **Mnemonic: STABLE PLAQUE = STENT (Smooth, Thick cap, Abundant collagen, Broad calcification, Low inflammation, Exertional symptoms)** Stable plaques are amenable to elective percutaneous intervention (PCI) with stent placement, as in this case. The risk of stent thrombosis is lower than with vulnerable plaques because the lesion is fibrotic and less thrombogenic. [cite:Robbins 10e Ch 11]