What causes a stroke?

Many roles, across the healthcare sector, interface with patients who have experienced a stroke, or are at risk of a stroke. Many people are also involved in the development of innovative new medicines and technologies for stroke prevention and management. In this article I’d like to share some key concepts.

There are two major types of stroke: one caused by a blocked artery in the brain (ischaemic stroke) and one caused by a leaking artery (haemorrhagic stroke).

Ischaemic strokes

Ischaemic strokes are the most common type. Here the blockage reduces or completely stops the flow of blood to the brain, depriving the brain tissue of oxygen, and causing the brain cells to die.

There are several causes for the blockage. The arteries in the brain may have become narrowed by atherosclerotic plaques (fatty cholesterol-containing deposits) and a blood clot (thrombus) forms on the plaque. A blood clot may also have formed elsewhere in the body and part of it may have broken off (embolus) and travelled via the blood stream to the arteries of the brain, where they become lodged, resulting in a blockage.

Ischaemic strokes are the most common type. Here the blockage reduces or completely stops the flow of blood to the brain

Treatment of ischaemic strokes involves removing the blockage (either using drugs that break down the blood clots; using a catheter to physically remove the clot; or inserting a stent into a narrowed artery).

Haemorrhagic strokes

Haemorrhagic strokes occur when the blood vessel in the brain splits or ruptures and blood leaks into the surrounding brain tissue. This is known as an intracranial haemorrhage or a cerebral haemorrhage and the main cause is hypertension (high blood pressure). Haemorrhagic strokes can also be caused when a brain aneurysm (the ballooning of a blood vessel) weakens and bursts open; or when the blood vessels in the brain have structural problems (eg arteriovenous malformations) that rupture. During a haemorrhagic stroke the leaking blood damages the surrounding brain cells; as well as depriving brain cells beyond the leak of blood and oxygen.

Haemorrhagic strokes occur when the blood vessel in the brain splits or ruptures and blood leaks into the surrounding brain tissue.

Treatment for a haemorrhagic stroke involves controlling the bleeding in the brain and reducing the pressure on the brain. Surgeons also repair malformed blood vessels and clamp aneurysms to prevent rupture.

Many factors can increase the risk of stroke: high blood pressure, high cholesterol, cigarette smoking, diabetes, obstructive sleep apnoea and cardiovascular disease. Stroke prevention strategies therefore include: controlling high blood pressure; lowering cholesterol; controlling diabetes; quitting smoking; eating a healthy diet and exercising. People with a history of ischaemic stroke may also be taking anti-platelet drugs and anti-coagulants.

Many factors can increase the risk of stroke: high blood pressure, high cholesterol, cigarette smoking, diabetes, obstructive sleep apnoea and cardiovascular disease

A stroke is a medical emergency requiring immediate attention. To determine whether someone is having a stroke you should act FAST. FAST is an acronym for Face; Arms; Speech and Time ie FACE = Ask the person to smile. Does one side of the face droop?; ARMS = Ask the person to raise both arms. Does one arm drift downwards?; SPEECH = Ask the person to repeat a simple phrase. Is their speech slurred or difficult to understand? TIME = If you see any of these signs phone emergency services (000).

Acting FAST is important because the longer a stroke remains untreated the higher the chance of brain damage. In hospital, suspected stroke patients undergo urgent brain imaging (CT or MRI) to assess whether the stroke is ischaemic or haemorrhagic. If appropriate reperfusion therapy is administered (eg tissue plasminogen activator) which breaks down the blood clot and restores blood flow to the brain.

Depending on which part of the brain is affected, and for how long the brain lacks oxygen, there can be a range of temporary or permanent complications including: paralysis; difficulty talking or swallowing; thinking difficulties or memory loss; pain or numbness; emotional problems and changes in behaviour. Rehabilitation incorporates a range of services including physical therapy, occupational therapy and speech therapy.

For further information consult the Clinical Guidelines for Stroke Management 2017, published by the Stroke Foundation.

Other articles in the Medical Education series:

Why does cancer occur?

Endocrinology explained

What is scurvy?

Medical Terminology Part 1

Medical Terminology Part 2

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