A stroke is a life-threatening medical emergency that happens when the blood supply to part of the brain is cut off. The blood supply may be cut off by a blood clot or from a burst blood vessel. A person having a stroke may lose control over their movement, perception and speech. They may also lose consciousness.

Clots near the brain
Over 80% of all strokes are due to blockage of the oxygen-rich blood flowing to the brain. Called ischaemic strokes, they are triggered by either a thrombus, which is a stationary clot that forms in a blood vessel, or an embolus, a clot that travels through the bloodstream and becomes lodged in a vessel. This type of stroke is often preceded by transient ischaemic attacks, or TIAs, which are episodes of inadequate blood flow that may produce these symptoms:
-- Sudden physical weakness
-- An inability to talk
-- Double vision
-- Dizziness

Symptoms of a TIA fully resolve within 24 hours. However, because these may be signs of an impending stroke, take them seriously and seek medical advice immediately.
With a TIA circulation and the vital oxygen supply are quickly restored and lasting brain and nerve damage is avoided. With a stroke, however, the interruption of blood flow lasts long enough to kill brain cells, producing irreversible damage.

Bleeding in the brain
The second basic type of stroke is bleeding stroke, or haemorrhagic stroke. It occurs when a brain aneurysm ruptures or when a weakened or inflamed blood vessel in the brain starts to leak. An aneurysm is a pouch that balloons out from a weakened spot of the wall of an artery. As blood flows into the brain, the build-up of pressure may either kill the tissue directly or destroy cells by impeding normal circulation and oxygen supply to the affected region. This typically produces an excruciating headache, sometimes followed by loss of consciousness.

In contrast to ischaemic strokes, which are generally survived, massive bleeding strokes are fatal about 80% of the time, while even smaller strokes due to bleeding into the brain cause death about 50% of the time.

Because of improved treatment and greater public awareness of the dangers of high blood pressure, the overall death rate from stroke is declining. Nonetheless, stroke remains the third leading cause of death in the UK behind heart disease and cancer. It is also the leading cause of disability and second only to Alzheimer’s disease as a cause of dementia.

Recovery from stroke depends on the extent and location of brain damage. Although about 25% of patients die within the first year of having their first stroke, some stroke victims recover fully. But in the vast majority of cases, there is lasting physical or mental disability. Weakened stroke victims are also more vulnerable to infectious diseases such as pneumonia. In addition, depression often follows a stroke and unless treated, it can significantly hinder recovery.