What is a stroke?
A stroke is damage to the brain caused by an interruption to it's blood supply or rupture of a blood vessel causing leakage of blood into the brain. It is a common cause of brain injury and can vary in severity from causing very mild symptoms, varying degrees of disability and even death. It is the brain equivalent of a heart attack.
What causes a stroke?
Cerebral infaction or Ischaemic stroke
The most common type of stroke is caused by blockage of an artery supplying the brain. This causes death or infarction of part of the brain that is deprived of blood and hence oxygen and nutrients. This kind of stroke is also known as ischaemic stroke.
Arteries can be blocked by several mechanisms but the most common ones are gradual narrowing of the artery by the deposit of fatty material (atheroma or atherosclerotic plaque) or the blockage of the artery by a clot that has travelled from the heart or from a larger artery upstream in the circulation. This is called embolism. Certain disorders of the rhythm of the heart or valve problems can cause clots to form in the heart. An artery with an ulcerated or irregular plaque can also be a site of clot formation.
Cerebral haemorrhage or Haemorrhagic stroke
Blood may leak into the brain from the rupture of a small artery damaged by high blood pressure, from aneurysms (abnormal balloon like swellings that form when an arterial wall is weakened) or from arterio- venous malformations (abnormal and weak blood vessels in the brain). The escaped blood forms a haematoma or clot which can be very large in size and causes destruction of adjacent parts of the brain by pressure and interruption of the blood flow. It can also cause other effects by raising the pressure in the brain as a whole.
Sometimes, the blood leaks into a space between the surface of the brain and a layer covering the brain. This is called a sub-arachnoid haemorrhage and is often due to the rupture of an aneurysm.
Bleeding can sometimes occur into part of the brain damaged by a cerebral infarct. This is called haemorrhagic transformation of an infarct.