A stroke can happen in two main ways. Either there is a blood clot or plaque that blocks a blood vessel in the brain or a blood vessel in the brain breaks or ruptures.
1. Blocked Artery (causes an ischaemic stroke)
A stroke that is caused by a blood clot is called an ischaemic stroke. In everyday life, blood clotting is beneficial. When you are bleeding from a wound, blood clots work to slow and eventually stop the bleeding. In the case of stroke, however, blood clots are dangerous because they can block arteries and cut off blood flow.
There are two ways an ischaemic stroke can occur.
1.1 Embolic Stroke
If a blood clot forms somewhere in the body (usually the heart) it can travel through the bloodstream to your brain. Once in your brain, the clot travels to a blood vessel that’s too small for it to pass through. It gets stuck there and stops blood from getting through. These kinds of strokes are called embolic strokes.
1.2 Thrombotic Stroke
As the blood flows through the arteries, it may leave behind cholesterol-laden ‘plaques’ that stick to the inner wall of the artery. Over time, these plaques can increase in size and narrow or block the artery and stop blood getting through. In the case of stroke, the plaques most often affect the major arteries in the neck taking blood to the brain. Strokes caused in this way are called thrombotic strokes.
2. Bleed in the brain (haemorrhagic)
Strokes caused by a break in the wall of a blood vessel in the brain are called haemorrhagic strokes. This causes blood to leak into the brain, again stopping the delivery of oxygen and nutrients. Haemorrhagic stroke can be caused by a number of disorders which affect the blood vessels, including long-standing high blood pressure and cerebral aneurysms.
An aneurysm is a weak or thin spot on a blood vessel wall. The weak spots that cause aneurysms are usually present at birth. Aneurysms develop over a number of years and usually don’t cause detectable problems until they break.
There are two types of haemorrhagic stroke:
– Intracerebral These two terms refer to areas of the brain where the stroke has occurred. In a subarachnoid haemorrhage, bleeding occurs under the thin, delicate membrane surrounding the brain. In an intracerebral haemorrhage, bleeding occurs within the brain itself.