A 52-year-old man with a 10-year history of essential hypertension presents with sudden onset left-sided weakness and speech difficulty. CT head shows an acute ischemic stroke in the middle cerebral artery territory. Which is the most common cause of arterial thrombosis in this patient?

Explanation

## Most Common Cause of Arterial Thrombosis in Stroke **Key Point:** Atherosclerotic plaque rupture with in-situ thrombosis is the single most common mechanism of acute arterial thrombosis, accounting for approximately 50–60% of ischemic strokes in the general population. ### Pathophysiology Atherosclerotic plaques in large and medium-sized arteries (especially carotid and cerebral arteries) undergo rupture when the fibrous cap is disrupted. This exposes the lipid-rich core and tissue factor to circulating blood, triggering the extrinsic coagulation pathway and platelet activation. The resulting thrombus occludes the vessel lumen, causing acute ischemia downstream. ### Why Atherothrombosis Dominates in This Case 1. **Long-standing hypertension** — a major driver of atherosclerosis and endothelial dysfunction 2. **Age 52** — atherosclerotic disease is prevalent in this age group 3. **Acute presentation** — sudden focal neurological deficit is typical of in-situ thrombosis rather than embolic phenomena 4. **No mention of atrial fibrillation or malignancy** — the other major thrombotic mechanisms are not suggested by the clinical context ### Frequency Comparison: Causes of Ischemic Stroke | Mechanism | Frequency | Key Features | | --- | --- | --- | | **Atherothrombosis** | 50–60% | Large/medium vessel disease; hypertension, smoking, dyslipidemia | | Cardioemboli | 20–30% | Atrial fibrillation, valvular disease, recent MI, endocarditis | | Small vessel disease (lacunar) | 10–15% | Hypertension, diabetes; deep brain infarcts | | Hypercoagulable/other | 5–10% | Malignancy, thrombophilia, vasculitis | **High-Yield:** In any patient with acute arterial thrombosis (stroke, MI, acute limb ischemia) and risk factors for atherosclerosis (age, hypertension, smoking, dyslipidemia), assume atherothrombosis is the mechanism unless clinical context strongly suggests embolism (e.g., new-onset atrial fibrillation, prosthetic valve, endocarditis). **Clinical Pearl:** The distinction matters for secondary prevention: atherothrombosis requires antiplatelet therapy (aspirin, clopidogrel) and intensive risk factor modification, whereas cardioemboli require anticoagulation. [cite:Harrison 21e Ch 297]