During a neurosurgery teaching session, the faculty asks: 'Which is the most common type of internal capsule stroke in terms of the vascular territory involved?' What is the correct answer?

Explanation

## Vascular Territory of Internal Capsule Strokes **Key Point:** The vast majority (>90%) of internal capsule strokes occur in the MCA territory, supplied by the lenticulostriate arteries (lateral perforating branches of the MCA). ### Vascular Supply of Internal Capsule Components | Internal Capsule Region | Primary Arterial Supply | Secondary Supply | Stroke Frequency | |------------------------|------------------------|------------------|------------------| | Anterior limb | Lenticulostriate (MCA) | Recurrent artery of Heubner (ACA) | 10–15% | | Genu | Lenticulostriate (MCA) | Recurrent artery of Heubner (ACA) | 20–30% | | Posterior limb | Lenticulostriate (MCA) | Posterior choroidal (PCA) | 50–60% | | Retrolenticular part | Posterior choroidal (PCA) | — | <5% | | Sublenticular part | Anterior choroidal (ACA) | — | Rare | **High-Yield:** The lenticulostriate arteries are end-arteries with minimal collateral circulation, making them the "stroke arteries" of the basal ganglia and internal capsule. They are exquisitely sensitive to hypertensive lipohyalinosis. ### Why MCA Territory Dominates 1. **Anatomical dominance:** The lenticulostriate arteries are the primary feeders to the internal capsule, arising directly from the M1 segment of the MCA. 2. **Hypertension vulnerability:** These arteries are most susceptible to lipohyalinosis and microaneurysm formation in chronic hypertension. 3. **Lacunar stroke predilection:** The internal capsule is the classic site of lacunar infarcts, which are predominantly MCA-territory events. **Clinical Pearl:** A patient with acute internal capsule stroke and hypertension almost always has an MCA-territory lacunar infarct. ACA, PCA, and vertebrobasilar strokes affecting the internal capsule are rare and usually indicate a different pathophysiology (e.g., cardioemboli, large-vessel atherosclerosis). **Mnemonic:** **MCA-IC** — **M**iddle **C**erebral **A**rtery supplies the **I**nternal **C**apsule (via lenticulostriate arteries).