What is a Stroke?
A stroke occurs when the blood supply to a part of the brain is suddenly cut off. This may be due to a blockage in a blood vessel, or when a blood vessel in the brain bursts, spilling blood into the spaces surrounding the brain cells. Brain cells (or neurones) need a constant supply of oxygen from the blood, and have no ability to respire anaerobically (i.e. without oxygen). If the blood supply is cut off for more than a few minutes the brain cells in the affected area of the brain become damaged. Some brain cells die immediately, whilst others may remain at risk of death for several hours, eventually either recovering or dying. When neurones die the result is an uncontrolled release of substances, which may result in toxic damage to other neurones. This in turn may damage other surrounding neurones and so on.
A stroke causes damage to a part of the brain, normally due to an interruption of its blood supply. The blood supply to the brain comes mainly from four arteries. These are the right and left carotid arteries and the right and left vertebral arteries. These main arteries branch into many smaller ones, which supply the entire brain with blood.
In a stroke, the amount of damage caused, and the area of the brain affected, depends upon the blood vessel involved. Symptoms and disabling effects vary greatly depending on the part of the brain affected and the extent of the brain damage.
If, for example a small branch artery is affected, then only a small area of the brain will be damaged and relatively minor symptoms are likely. However if a main carotid artery is affected, then severe symptoms or death may result.
Dissection of the relevant blood vessel is also an important cause, as it occurs in 1 in 4 people with strokes (1 in 5 under the age of 50). It is diagnosed on MRI, angiogram or Doppler investigation. Treatment is anticoagulation(such as with Warfarin), and patients can do well.
15-20% of people have a significant aphasia following a stroke and 10% have a cognitive defect affecting memory, perception, intellect and other higher cerebral functioning.
