A stroke occurs when blood supply to part of the brain is interrupted. This event results in brain damage. Functions which are normally controlled by the damaged brain become affected suddenly and will not function properly. As stroke is a potentially life-threatening disease, it is important to seek early treatment.
There are two types of stroke: Blockage (ischemic/infarct) and bleeding (haemorrhagic).
An ischemic stroke is the more common form of stroke. It occurs when an artery supplying blood to a part of the brain is blocked. The blockage is due to a blood clot being formed within an artery (thrombotic stroke) or a blood clot that travels to the brain from the heart or another artery supplying the brain (embolic stroke). The blood clot that forms within an artery usually does so at places that have underlying atherosclerosis
Shows an artery with smooth endothelium (inner part of the artery wall) damaged or torn.
When the endothelium layer is damaged or torn, cholesterol will be able to deposit itself into the core of the artery. Platelets will stick to the surface of the damaged tissue. Fig. 2 shows the development of the process.
Over a period of time, the lumen of the artery will get narrower, resulting in less blood flow through it. A blood clot (thrombus) could then develop, further narrowing or completely blocking blood flow through the artery, causing a stroke.
A blood clot that travels from the heart or from an area of atherosclerosis through the artery to the brain is called an embolus. When an embolus reaches a part of the brain artery that it is not able to pass through, it will block the artery and stroke occurs. Atrial fibrillation (irregular heart beat) can cause blood clots to be formed within the heart, which can then embolise.
Another form of stroke is haemorrhagic (bleeding). A haemorrhagic stroke occurs when an artery bursts within the brain, causing an intracerebral haemorrhage. Less commonly, it bursts into the space around the brain, causing a subarachnoid haemorrhage. The main causes are uncontrolled or severe hypertension (high blood pressure), structural problems with the blood vessels of the brain like aneurysm and arteriovenous malformation (AVM).