## Most Common Site of Arterial Occlusion in Acute Ischemic Stroke **Key Point:** The middle cerebral artery (MCA) is the most common site of arterial occlusion in acute ischemic stroke, accounting for approximately 50–60% of all ischemic strokes. ### Anatomical Basis The MCA is the largest branch of the internal carotid artery and supplies: - Lateral cerebral hemispheres (motor and sensory cortex) - Broca's area (dominant hemisphere) - Wernicke's area (dominant hemisphere) - Basal ganglia and internal capsule ### Distribution of Ischemic Strokes by Arterial Territory | Arterial Territory | Frequency | Clinical Presentation | | --- | --- | --- | | **MCA** | 50–60% | Contralateral hemiparesis, hemisensory loss, aphasia (dominant) | | **ACA** | 5–10% | Contralateral lower limb weakness, abulia | | **PCA** | 5–10% | Homonymous hemianopia, visual field defects | | **Vertebrobasilar** | 10–20% | Brainstem signs, cerebellar ataxia, cranial nerve palsies | **High-Yield:** MCA occlusion is the most common cause of acute ischemic stroke in both cardioembolic and large-vessel atherosclerotic disease patterns. ### Why MCA Dominance? 1. **Hemodynamic factors:** Direct continuation of the internal carotid artery 2. **Vessel caliber:** Largest intracranial branch 3. **Thromboembolic predilection:** Cardioemboli preferentially lodge in the MCA due to flow dynamics **Clinical Pearl:** MCA occlusion typically presents with the classic "lacunar-plus" syndrome or complete hemispheric stroke with contralateral motor and sensory deficits, often accompanied by language disturbance (if dominant hemisphere) or neglect (if non-dominant hemisphere). ### Imaging Findings - **CT:** May be normal in hyperacute phase; hypodensity in MCA territory after 6–12 hours - **MRI DWI:** Hyperintensity in MCA distribution (cortical and subcortical white matter) - **CTA/MRA:** Direct visualization of MCA occlusion [cite:Harrison 21e Ch 296]
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