A 62-year-old woman from Bangalore with hypertension and diabetes presents with acute onset left-sided weakness and expressive aphasia 6 hours after symptom onset. Non-contrast CT head is unremarkable. MRI brain DWI shows multiple small hyperintense foci scattered throughout the left hemisphere in a cortical and subcortical distribution, with corresponding ADC restriction. MR angiography reveals no large vessel occlusion. What is the most likely etiology of this acute ischemic stroke?

Explanation

## Clinical and Imaging Analysis ### Key Distinguishing Features | Feature | Finding in This Case | Significance | |---------|----------------------|--------------| | DWI lesion distribution | Multiple scattered foci (cortical + subcortical) | Suggests embolic mechanism | | Vascular territory | Entire left hemisphere (not limited to single arterial territory) | Inconsistent with single arterial occlusion | | MRA findings | No large vessel occlusion | Rules out proximal arterial thrombosis | | Lesion size | Multiple small infarcts | Typical of cardioembolic shower | | Clinical presentation | Aphasia + hemiparesis | Large cortical involvement | ## Stroke Etiology Classification (TOAST Criteria) ```mermaid flowchart TD A[Acute ischemic stroke]:::outcome --> B{Large vessel occlusion on imaging?}:::decision B -->|Yes| C[Atherosclerotic or embolic]:::outcome B -->|No| D{Multiple scattered infarcts?}:::decision D -->|Yes| E[Cardioembolic]:::outcome D -->|No| F{Single small infarct in deep territory?}:::decision F -->|Yes| G[Lacunar/Small vessel disease]:::outcome F -->|No| H[Other/Undetermined]:::outcome ``` **Key Point:** Multiple acute infarcts in different vascular territories on DWI is the classic imaging signature of cardioembolic stroke, reflecting emboli from a cardiac source showering into multiple branches of the cerebral circulation. **High-Yield:** The **scattered, multifocal DWI hyperintensities** across cortical and subcortical regions in different vascular territories is pathognomonic for cardioembolic etiology. This pattern reflects multiple emboli from a cardiac source (most commonly atrial fibrillation). **Mnemonic: CARDIO-EMBOLIC STROKE IMAGING = "SHOWER OF INFARCTS"** - Multiple lesions in different territories - Often cortical (gray matter predilection) - Acute DWI hyperintensity - Rapid onset - Often large vessel territory involvement (MCA, ACA, PCA) - Often recurrent if source not treated ## Why Cardioembolic? 1. **Multifocal DWI lesions** — emboli lodge in multiple arterial branches simultaneously 2. **Scattered distribution** — not confined to single arterial territory (unlike atherosclerotic occlusion) 3. **Cortical involvement** — emboli preferentially lodge at arterial bifurcations in cortical branches 4. **Normal MRA** — rules out proximal arterial pathology; source must be cardiac ## Next Steps in Workup - Continuous cardiac monitoring (Holter, telemetry) to detect atrial fibrillation - Transthoracic echocardiography (TEE if TTE inconclusive) to identify cardiac source - Consider PFO screening if no obvious cardiac source and patient age < 60 [cite:Harrison 21e Ch 435; Robbins 10e Ch 28]