The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of blood and oxygen. As a result of the deprived blood and oxygen, the cells of that part of the brain die and the part of the body that it controls stops working. Typically, a cholesterol plaque in one of the brain's small blood vessels ruptures and starts the clotting process.
Risk factors for narrowed blood vessels in the brain are the same as those that cause narrowing blood vessels in the heart and heart attack (myocardial infarction). These risk factors include:
Another type of stroke may occur when a blood clot or a piece of atherosclerotic plaque (cholesterol and calcium deposits on the wall of the inside of the heart or artery) breaks loose, travels through the bloodstream, and lodges in an artery in the brain. When blood flow stops, brain cells do not receive the oxygen and glucose they require to function and a stroke occurs. This type of stroke is referred to as an embolic stroke. For example, a blood clot might originally form in the heart chamber as a result of an irregular heart rhythm, like atrial fibrillation. Usually, these clots remain attached to the inner lining of the heart, but occasionally they can break off, travel through the bloodstream (embolize), block a brain artery, and cause a stroke. An embolism, either plaque or clot, may also originate in a large artery (for example, the carotid artery, a major artery in the neck that supplies blood to the brain) and then travel downstream to clog a small artery within the brain.
A cerebral hemorrhage occurs when a blood vessel in the brain ruptures and bleeds into the surrounding brain tissue. A cerebral hemorrhage (bleeding in the brain) causes stroke symptoms by depriving blood and oxygen to parts of the brain in a variety of ways. Blood flow is lost to some cells. Additionally, blood is very irritating and can cause swelling of brain tissue (cerebral edema). Edema and the accumulation of blood from a cerebral hemorrhage increases pressure within the skull and causes further damage by squeezing the brain against the bony skull. This further decreases blood flow to brain tissue and its cells.
In a subarachnoid hemorrhage, blood accumulates in the space beneath the arachnoid membrane that lines the brain. The blood originates from an abnormal blood vessel that leaks or ruptures. Often this is from an aneurysm (an abnormal ballooning out of the blood vessel). Subarachnoid hemorrhages usually cause a sudden severe headache, nausea, vomiting, light intolerance, and stiff neck. If not recognized and treated, major neurological consequences, such as coma, and brain death may occur.
Another rare cause of stroke is vasculitis, a condition in which the blood vessels become inflamed causing decreased blood flow to parts of the brain.
There appears to be a very slight increased occurrence of stroke in
people with migraine headache. The mechanism for migraine or
vascular headaches includes narrowing of the brain blood vessels.
Some migraine headache episodes can even mimic stroke with loss
of function of one side of the body or vision or speech problems. Usually, the
symptoms resolve as the headache resolves.
Many factors can increase your stroke risk. Some factors can also increase your chances of having a heart attack. Potentially treatable stroke risk factors include:
Lifestyle risk factors
Medical risk factors
Other factors associated with a higher risk of stroke include:
Symptoms of a stroke often appear without warning.
The main symptoms of stroke are:
Strokes can lead to long-term health problems. Depending on how quickly it is diagnosed and treated, an individual can experience temporary or permanent disabilities in the aftermath of a stroke.
In addition to the persistence of the problems listed above, people may also experience the following:
Symptoms vary and may range in severity.
The acronym F.A.S.T. is a way to remember the signs of stroke, and can help identify the onset of stroke:
The faster a person with suspected stroke receives medical attention,
the better their prognosis will be, and the less likely they will be to
experience permanent damage or death.
Strokes onset rapidly and will often occur before an individual can be seen by a doctor for a proper diagnosis.
For a person experiencing a stroke to get the best diagnosis and treatment possible, they should be treated at a hospital within 3 hours of their symptoms first appearing.
There are several different types of diagnostic tests that doctors can use to determine which type of stroke has occurred:
It is only possible to confirm the type of stroke someone has had by
giving them a brain scan in a hospital environment.
As ischemic and hemorrhagic strokes have different causes, both require different forms of treatment.
It is not only important that the type of stroke is diagnosed quickly to reduce the damage done to the brain, but also because a treatment suitable for one type of stroke may be harmful when treating different type.
Ischemic strokes are caused by arteries being blocked or narrowed, and so treatment focuses on restoring an adequate flow of blood to the brain.
Treatment starts with drugs that break down clots and prevent others from forming. Aspirin can be given, as can an injection of tissue plasminogen activator (TPA). TPA is very effective at dissolving clots but needs to be injected within 4.5 hours of stroke symptoms starting.
Emergency procedures include administering TPA directly into an artery in the brain or using a catheter to physically remove the clot. Research is still ongoing as to the benefit of these procedures.
There are other procedures that can be carried out to decrease the risk of strokes or TIAs. A carotid endarterectomy involves a surgeon opening the carotid artery and removing any plaque that might be blocking it.
Alternatively, an angioplasty involves a surgeon inflating a small balloon in a narrowed artery via catheter and then inserting a mesh tube called a stent into the opening. This prevents the artery from narrowing again.
Hemorrhagic strokes are caused by blood leaking into the brain, so treatment focuses on controlling the bleeding and reducing the pressure on the brain.
Treatment can begin with drugs given to reduce the pressure in the brain, control overall blood pressure, prevent seizures and prevent sudden constrictions of blood vessels.
If an individual is taking blood-thinning anticoagulants or an antiplatelet medication like warfarin or clopidogrel, they can be given drugs to counter the effects of the medication or blood transfusions to make up for blood loss.
Surgery can be used to repair any problems with blood vessels that have led or could lead to hemorrhagic strokes. Surgeons can place small clamps at the base of aneurysms or fill them with detachable coils to stop blood flow and prevent rupture.
If the hemorrhage is caused by arteriovenous malformations (AVMs), surgery can also be used to remove them if they are not too big and not too deep in the brain. AVMs are tangled connections between arteries and veins that are weaker and burst more easily than other normal blood vessels.
The best way to prevent a stroke is to address the underlying causes. This is best achieved through lifestyle changes, including:
Eating a nutritious diet means including plenty of fruits, vegetables, and healthy whole grains, nuts, seeds, and legumes. Be sure to eat little or no red or processed meat and limit intake of cholesteroland saturated fats. Minimize salt intake to support healthy blood pressure.
Other measures taken to help reduce the risk of stroke include:
As well as these lifestyle changes, a doctor can help to reduce the risk of future ischemic strokes through prescribing anticoagulant or antiplatelet medication.
In addition, arterial surgery can also be used to lower the risk of
repeat strokes, as well as some other surgical options still being studied.