Ischaemic stroke and thromboembolism
Ischaemic stroke, the blocked-artery type, most often happens when a clot cuts off the blood supply to part of the brain.
Remember
Around 85% of strokes are ischaemic, and an ischaemic stroke is usually caused by a clot that formed elsewhere and travelled in the arteries to block an artery in the brain.
Memory aid
ischaemic means the pipe is blocked, haemorrhagic means the pipe has burst
Use the pipe picture to tell the two stroke types apart: a blocked pipe is ischaemic and a burst pipe is haemorrhagic.
A stroke is a loss of the blood supply to one portion of the brain, and there are two main types. In an ischaemic stroke an artery is blocked, most often by a clot, and the supply is cut off. In a haemorrhagic stroke a vessel bursts and bleeds. Memory aid: ischaemic means the pipe is blocked, haemorrhagic means the pipe has burst.
Ischaemic strokes are the commonest type, making up around 85% of strokes. Haemorrhagic strokes make up around 15%.
The clot usually formed somewhere else, such as the heart or a diseased neck artery, and then travelled through the arteries to the brain. This is called a thromboembolism: a thrombus is a clot, and an embolus is a clot (or other material) that breaks off and travels. Less often, the clot forms on a diseased part of the brain's own arteries. This is thrombosis in situ, meaning a clot forming on a diseased artery.
Once the artery is blocked, the area beyond it loses oxygen and glucose. Brain cells then cannot make energy (ATP). If flow is not restored, the tissue dies, and this is called infarction.
An embolus blocks an artery abruptly, so the symptoms appear at full strength within minutes, and embolic strokes more often happen in the daytime. Thrombosis in situ (a clot forming on a diseased artery) tends to cause a slower, stepwise evolution, and these strokes are often first noticed on waking.
The two stroke types need opposite treatment, so a CT head scan is done urgently to rule out bleeding before clot treatment starts.
Key facts
- Commonest type
- ischaemic strokes make up around 85% of strokes, and haemorrhagic strokes around 15%.
- Mechanism
- an artery is blocked, most often by a clot, and the blood supply to part of the brain is cut off.
- Usual source
- the clot usually formed elsewhere, such as the heart or a diseased neck artery, and travelled to the brain.
- Embolic onset
- the symptoms appear at full strength within minutes, and embolic strokes more often happen in the daytime.
- Thrombotic onset
- thrombosis in situ tends to evolve slowly or in steps and is often first noticed on waking.
- Why it matters
- the two stroke types need opposite treatment, so a CT head scan is done urgently to rule out bleeding.
Exam traps
- A vessel in the brain that ruptures and lets blood compress the surrounding brain tissue describes a haemorrhagic stroke, not an ischaemic one, because in an ischaemic stroke an artery is blocked rather than burst.
- A transient ischaemic attack, a temporary blockage of an artery, is not a stroke by definition, because the symptoms resolve completely and there is no infarction on imaging.
- Cerebral venous sinus thrombosis, a clot in a vein that drains blood from the brain, affects drainage rather than arterial supply, and it is uncommon compared with arterial stroke.
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