There are two different kinds of stroke, an ischaemic stroke which is caused by a blockage preventing blood reaching parts of the brain and
haemorrhagic stroke which is caused by blood seeping into the brain.
Ischaemic Stroke
Seventeen out of twenty strokes are ischaemic strokes. These occur when blockages in arteries severely restrict the flow of blood to the brain.
There are two main types of ischaemic stroke:
- Thrombotic stroke. Thrombotic strokes occur when a blood clot forms in an artery that supplies blood to the brain. Clot formation is usually due to
a condition known as atherosclerosis in which arteries become clogged by cholesterol-containing fatty deposits or plaques. Thrombotic strokes can occur
in the carotid arteries of the neck as well as in other arteries;
- Embolic stroke. Embolic strokes occur when a blood clot forms in a blood vessel which is some distance from the brain, usually in the heart, and is then
circulated to the brain where it gets stuck in one of the narrower arteries. These clots are called emboli, they are often caused by irregular beating of
the heart. An abnormal heartbeat can lead to poor blood flow and the formation of a clot.
Haemorrhagic stroke
Haemorrhagic strokes occur when a blood vessel in the brain leaks or ruptures. These haemorrhages can occur for a number of reasons including uncontrolled
blood pressure (hypertension) and weaknesses in the blood vessel walls (aneurysms).
There are two types of haemorrhagic stroke:
- Intracerebral haemorrhage. Intracerebal haemorrhages occur when a blood vessel in the brain bursts and blood spills into the brain which damages the cells.
Brain cells that lie beyond the spillage are damaged by being deprived of blood. High blood pressure is the most common cause of this kind of stroke- high
blood pressure may cause small arteries inside the brain to become brittle which increases the chances of them cracking and rupturing.
- Subarachnoid haemorrhage. Subarachnoid haemorrhages occur when bleeding begins in a large artery on or near the membrane surrounding the brain and then spills into the space between the surface of the brain
and the inside of the skull. This type of stroke is often signalled by a sudden and severe headache.
