Carotid Artery Stenosis

Carotid stenosis causes stroke by embolism, not by starving the brain of flow

Atherosclerotic plaque narrows the internal carotid artery lumen, but the brain is protected by collateral flow through the circle of Willis, so even a tight stenosis rarely causes ischaemia through flow reduction alone. The real danger is that the plaque surface is a nucleus for platelet aggregation and cholesterol or thrombus debris, fragments of which embolise distally into the cerebral or retinal circulation and lodge in smaller vessels. This embolic, rather than haemodynamic, mechanism is why symptom risk tracks plaque instability as much as luminal narrowing.