What is a Stroke?
The most common form of a Stroke is the result of a sudden disruption of the flow of blood to parts of the brain.
When blood cannot reach parts of the brain, the oxygen supply to those areas is cut off and the brain cells die (infarct).
Less frequently, blood vessels burst and blood spreads into nearby brain areas (haemorrhage). The result of these processes is a Stroke.
Functions normally controlled by these damaged brain areas are affected. In many cases, unconsciousness and/or partial paralysis may occur. This is often the immediate outward sign that a Stroke has occurred.
There are two different types of Stroke.
- Ischaemic Stroke and
- Haemorrhagic 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, clots are dangerous because they can block arteries and cut off blood flow. Ischaemic Stroke is the most common type of Stroke (80% – 85% of Strokes are ischaemic). An Ischaemic Stroke is caused when a clot blocks or ‘plugs’ a blood vessel in the brain. There are two ways that a clot Stroke can occur:
- An embolic Stroke occurs when a blood clot forms somewhere in the body and travels through the blood stream to the brain.
- A thrombotic Stroke occurs when blood vessels narrow as a result of blood fat, cholesterol or calcium, which grow to completely block the blood vessel.
A haemorrhagic Stroke is caused when a blood vessel in the brain breaks or ‘erupts’. There are two types of Haemorrhagic Stroke – a subarachnoid haemorrhage and an intracerebral haemorrhage.
- An intracerebral haemorrhage, which is the more common form, involves bleeding within the brain tissue itself.
- With a subarachnoid haemorrhage bleeding occurs in the space around the brain. Often this is due to an aneurysm – a weak or thin spot on a blood vessel wall.