## Most Common Site of Arterial Occlusion in Acute Ischemic Stroke **Key Point:** The middle cerebral artery (MCA) is the most frequently occluded vessel in acute ischemic stroke, accounting for approximately 50–60% of all acute ischemic strokes. ### Anatomical and Hemodynamic Basis The MCA is the direct continuation of the internal carotid artery (ICA) and receives the largest share of cerebral blood flow. Its large caliber and favorable hemodynamic position make it the most common site for: - Thromboembolism from cardiac sources - In-situ atherosclerotic thrombosis - Artery-to-artery embolism from proximal ICA disease ### Frequency of Arterial Occlusion by Vessel | Artery | Frequency | Territory Affected | Clinical Presentation | |--------|-----------|-------------------|----------------------| | **MCA** | **50–60%** | **Lateral hemisphere** | **Contralateral hemiparesis, hemisensory loss, aphasia (dominant), neglect (non-dominant)** | | ACA | 5–10% | Medial hemisphere, anterior corpus callosum | Contralateral lower limb weakness, abulia, urinary incontinence | | PCA | 10–15% | Occipital and temporal lobes | Contralateral homonymous hemianopia, visual agnosia | | VA/Basilar | 10–15% | Brainstem, cerebellum, occipital lobe | Vertigo, ataxia, cranial nerve deficits, locked-in syndrome | **High-Yield:** MCA occlusion is the most common cause of acute ischemic stroke and the most frequent indication for thrombolytic therapy and mechanical thrombectomy. ### MRI Findings in MCA Stroke Diffusion-weighted imaging (DWI) shows restricted diffusion (hyperintense signal) within minutes of symptom onset, corresponding to the MCA vascular territory: - Lateral lenticulostriate territory (putamen, external capsule) - Insular cortex - Lateral temporal and parietal lobes - Frontal operculum (if proximal MCA occlusion) **Clinical Pearl:** Non-contrast CT is often normal in the hyperacute phase of ischemic stroke (first 6–12 hours), whereas DWI-MRI detects ischemia within minutes. This makes MRI superior for early diagnosis and patient selection for thrombolytic therapy. **Mnemonic — MCA Territory Stroke Deficits: LATCH** - **L**ower face weakness (contralateral) - **A**phasic/Agraphic (if dominant hemisphere) - **T**humb and finger weakness - **C**ontralateral sensory loss - **H**omonymous hemianopia (if extensive) [cite:Harrison 21e Ch 379]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.