There are two types of stroke, each of which have a number of possible causes:
Atherosclerosis or hardening and narrowing of the arteries causes an ischaemic stroke. A blood clot (thrombus) forms in such a narrowed artery and obstructs the flow of blood to a part of the brain. However, unlike disease of the vessels of the heart (the coronary arteries), atherosclerosis of vessels of the brain itself is not very common.
The commonest cause of ischaemic stroke (infarction) is a blood clot formed in another part of the body, usually the large blood vessel in the neck (the carotids), the aortic arch, or the heart. This clot (embolus) breaks loose and travels in the blood stream until it blocks an artery that supplies blood to the brain. This is probably the commonest cause of major stroke
Very commonly, chronic hypertension leads to changes in the walls of small blood vessels which supply the deep parts of the cerebral hemispheres. These may sometimes block and cause small strokes, with variable results (may clear rapidly or there may be permanent weakness).
A haemorrhagic stroke occurs when an artery inside the brain suddenly starts bleeding (cerebral haemorrhage).
This type of stroke can also occur when an artery in the surrounding tissues on the surface of the brain starts to bleed (subarachnoid haemorrhage).
The usual cause of subarachnoid haemorrhage is that an artery with a weak point in its wall blows this out to form a balloon- or bubble-like swelling (an aneurysm), which eventually ruptures.
However, high blood pressure or hypertension (over 140/90 mm Hg) is the most common cause of the bleeding into the brain. The constant force of uncontrolled raised blood pressure weakens the walls of blood vessels to a point when the artery is torn open and bleeds.
(Reviewed by Dr J. Carr, FCP(SA) Neurology, MSc(Med))
Treating a stroke
Symptoms of a stroke
Risk factors for having a stroke