Strokes explained

A stroke occurs when a part of the brain is injured from a disturbance in its blood supply. Learn how to recognise the warning signs and minimise the risks

  • Types of stroke
  • Risk factors for stroke
  • Symptoms and diagnosis
  • Treatment and prevention
    Stroke is a very common condition, with about 100,000 people having a first stroke every year in the UK. Most of these people are over 55, but a stroke can happen at any age; the risks increase with age and they are also slightly more common in women than men.

    A stroke occurs when, for a number of reasons, an area of the brain is deprived of oxygen. The nerve cells (neurones) in the affected area of the brain can't function and die within minutes. And when nerve cells can't function, the part of the body controlled by these cells can't function either. The devastating effects of stroke are often permanent; dead brain cells cannot regrow.

    Types of stroke
    Stroke is actually a collective term for many different types of brain injuries. There are two main types:
    1. Ischaemic
    Ischaemic strokes are the most common type, accounting for about 85 per cent of the total. An ischaemic stroke, or cerebral infarction, occurs when an artery carrying blood to supply part of the brain is suddenly blocked, usually by a clot. Clotting is a necessary function: it stops bleeding and allows repair of damaged areas of arteries or veins. However, when blood clots develop in the wrong place within an artery, they can interfere with blood flow to the brain. You are more likely to have clotting problems the older you get.

    Ischaemic strokes caused by blood clots include two kinds:

  • Cerebral embolism, or embolic stroke - this means a blood clot forms somewhere in the body (either from the heart or one of the arteries in the chest or neck that supply the brain) and travels through the bloodstream to become lodged in an artery supplying the brain.
  • Cerebral thrombosis, or thrombotic stroke - this means the blood flow ceases because of a blockage that originates in one or more of the arteries supplying blood to the brain or within the brain itself. The blood clot in one of the cerebral arteries eventually grows large enough to block blood flow.

    2. Haemorrhagic
    A haemorrhagic stroke, or cerebral or subarachnoid haemorrhage, occurs when a blood vessel in the brain bursts, spilling blood into the substance of the brain or into the spaces surrounding brain cells. The two kinds of haemorrhagic stroke are:

  • Intracerebral haemorrhage - this is when there is bleeding from vessels within the brain itself.
  • Subarachnoid haemorrhage - this is usually from the rupture of an aneurysm or a malformation of blood vessels on or near the thin, delicate membrane surrounding the brain.

    Brain cells die when they no longer receive oxygen and nutrients from the blood, but they are also damaged by sudden bleeding into or around the brain. When blood flow to the brain is interrupted, some brain cells die immediately, while others remain at risk of dying. That's why immediate treatment is critical.

    Haemorrhagic stroke accounts for nearly 15 per cent of all strokes and is more frequent among the young and people with high blood pressure. One common cause is a bleeding aneurysm (weak or thin spot on an artery wall). Over time, these weak spots stretch or balloon out under high arterial pressure. The thin walls of these ballooning aneurysms can rupture and spill blood into the space surrounding brain cells.

    Haemorrhage can also occur when arterial walls break open. Plaque-encrusted artery walls eventually lose their elasticity and become brittle, thin and prone to cracking. High blood pressure increases the risk that a brittle wall will give way.

    When an artery in the brain bursts, blood spews into the surrounding tissue. Brain neurones generally don't come into direct contact with blood; the contact upsets the blood supply and the delicate chemical balance neurones require to function.

    Risk factors for stroke
    There are a number of factors that increase your risk of having a stroke, and many strokes are preventable. The most well-known risk factors include:

  • High blood pressure or hypertension. If high blood pressure is untreated it may damage the walls of the arteries that may then lead to stroke. This is one of the reasons why everyone should have their blood pressure measured from time to time, especially later in life.
  • Smoking. There are many health risks for smokers, and one of these is an increased risk of having a stroke due to damage to the arteries and its contribution to high blood pressure.
  • Diabetes. Those who have diabetes are more likely to have atherosclerosis - 'furred up' arteries - and high blood pressure, both of which contribute to the risk of stroke.
  • Age. Ten per cent of stroke victims are under 45. Women under 45 are more likely to have a stroke than a heart attack. For every decade after 55, your risk of stroke doubles. Two thirds of all strokes occur in people over 65. People over 65 also have a seven-fold greater risk of dying from stroke than the general population.
  • Diet. A high salt diet can contribute to high blood pressure, while a diet rich in sugary, fatty foods can cause arteries to 'fur up'.
  • Family history. Stroke seems to run in some families, and family members may share a genetic predisposition for hypertension or diabetes, both of which are risk factors for stroke. Of course, shared lifestyle habits may also be a factor.
  • Ethnic group. For reasons that are not well understood there is a higher risk of stroke in Asians, Africans and Afro-Caribbeans.

  • Arteriovenous malformation (AVM). An additional risk factor applies only to people subject to one particular type of stroke. A person with an AVM is at increased risk for haemorrhagic stroke. AVMs are a tangle of defective blood vessels and capillaries in the brain; they have thin walls and are more likely to rupture.
  • Recurrence. Having already had a stroke puts you at higher risk for another one. Recurrent stroke is frequent - about 25 per cent of people who recover from a first stroke will have another one within five years. The risk of severe disability or death from stroke increases with each stroke recurrence, and the risk of recurrence is greatest soon after a stroke. About three per cent of stroke patients will have another stroke within 30 days of their first stroke, and one third of recurrent strokes take place within two years of the first stroke.
  • Heart disease. Heart disease, including abnormal rhythms of the heart that may lead to blood clots forming in the heart then breaking away, increases the risk of stroke.
  • Other risk factors include heavy alcohol consumption, high blood-cholesterol levels and illicit drug use.

    Women and the risk of stroke
    Some risk factors for stroke apply only to women, such as pregnancy, childbirth and menopause. These risk factors are tied to hormonal fluctuations and changes that affect a woman in different stages of life.

    Pregnancy increases the risk of stroke as much as three to 13 times. However, since the risk of stroke in women of childbearing age is very small to begin with, a moderate increase in risk during pregnancy is still a relatively small risk. Pregnancy and childbirth cause strokes in approximately eight in 100,000 women, but 25 per cent of those strokes end in death.

    Some studies indicate that menopause can increase a woman's risk of stroke. However, hormone replacement therapy may reduce some of the effects of menopause and decrease stroke risk. Oestrogen's benefit in stroke prevention, as in prevention of heart disease, may stem from its role in cholesterol control.

    Symptoms of stroke
    Strokes affect different people in different ways, depending on the type of stroke, the area of the brain affected and the extent of the brain injury. Brain injury from a stroke can affect the speech, motor activity, cognitive ability, behaviour, memory and emotions. Paralysis or weakness on one side of the body is common.

    Strokes strike suddenly, and symptoms include:

  • Numbness or weakness of the face, arm or leg, especially on one side of the body
  • Confusion
  • Difficulty speaking or understanding speech
  • Trouble seeing in one or both eyes
  • Dizziness, or loss of balance or co-ordination
  • Sudden, uncharacteristic and severe headache

    Since the symptoms appear suddenly and there is usually more than one, you can probably distinguish stroke from other causes of dizziness or headache. You may experience other, less common symptoms, including sudden nausea, fever and vomiting. Sometimes, a stroke is accompanied by fainting, convulsions and/or coma.

    If you experience symptoms, it is probably best to call an ambulance to get to a hospital immediately. The doctors there may want to give you some kind of medication as soon as possible after the event.

    Transient ischaemic attack (TIA)
    A transient ischaemic attack (TIA), sometimes called a mini-stroke, starts just like a stroke, lasts a few minutes and leaves no lasting damage. But you can't ignore it - you have no way of telling if the episode is a TIA of a full-blown stroke. And even it is just a TIA, take heed: it can be a warning that you are at risk of a more serious stroke. About one third of those who have a TIA will have an acute stroke sometime in the future. Your chances increase if you have other risk factors.