In an ischemic stroke, the blood supply to part of the brain is cut off. This happens because of atherosclerosis in a blood vessel feeding part of the brain or a blood clot has blocked a blood vessel. Blood clots can also travel to the brain from another artery or from the heart.
This type of stroke can be caused by a blockage anywhere along the arteries feeding the brain. The blockages can occur for many reasons, including:
- The build up of fatty material (atheroma) along artery walls that cuts down blood flow
- Breaking off of an atheroma from the artery wall. It can flow with the blood getting stuck in a smaller artery causing a blockage.
- Blood clots that break loose from the heart or one of its valves, known as an emboli. They can go through the arteries to the brain, where they lodge causing an embolic stroke or cerebral embolism. This is most common in people who have recently had heart surgery or who have defective heart valves or abnormal heart rhythms.
- Inflammation or an infection that narrows blood vessel that leads to the brain
- Drugs such as cocaine and amphetamines, which can narrow blood vessels
- Suddenly falling blood pressure. Although a sudden drop in blood pressure usually causes a person to faint, it can lead to a stroke if it is severe and lasts a long time. This happens when someone loses a lot of blood from an injury or surgery, has a heart attack or has an abnormal heart rate or rhythm.
Strokes may also cause swelling in the brain. The resulting pressure can damage brain tissue more, making neurologic problems worse even if the stroke itself doesn't enlarge.
Most strokes happen suddenly and damage the brain within minutes. In rarer cases, a stroke may get worse for several hours to a day or two as a steadily enlarging area of the brain dies (stroke in evolution). In this case, the stroke is usually (although not always) interrupted by stable periods when the area temporarily stops getting bigger or some improvement occurs.
The common symptoms of stroke include:
- Loss of (or abnormal) sensations in an arm, leg or one side of the body
- Weakness or paralysis of an arm or leg or one side of the body
- Partial loss of vision or hearing
- Double vision
- Dizziness
- Slurred speech
- Problems thinking of or saying the right word
- Inability to recognize parts of the body
- Imbalance and falling
A doctor can often know that a stroke occurred based on a detailed history of events plus a physical examination. The diagnosis can be confirmed with tests including computer tomography (CT) scanning and magnetic resonance imaging (MRI). Newer MRI scans can show a stroke within minutes of symptoms (and at times, even before symptoms start). Once the doctor is sure the patient has had an ischemic stroke, it is important to identify the type of stroke and what caused it.
Treatment of a stroke varies depending on the cause -- a blood clot from the heart, a blockage in a large artery in the neck, a narrowing of a moderate sized artery in the brain or a blockage of a very small vessel in the head.
Diagnostic testing will depend on the patient and the symptoms. Some will need images of the chambers of the heart (an echocardiogram). Others will need an ultrasound of the vessels in the neck (duplex scan) or the head (transcranial Doppler). Still others may need sophisticated blood tests to look for a tendency for the blood to clot more easily.
A stroke's impact varies widely, depending on how severe it was and what parts of the brain it affected. Many people recover all or most of their ability to function in daily life after a stroke. Others can be left unable to move, speak or eat normally.
In the first few days, doctors generally can't predict whether a patient will improve or worsen. About half of the people who have one-sided paralysis and most with less severe symptoms recover some function before leaving the hospital. They can eventually take care of their basic needs. They may be able to think clearly and walk adequately, although their use of an affected arm or leg may be limited to some degree. Use of an arm is more often limited than use of a leg.
About 20% of the people who have a stroke die in the hospital. The percentage is higher among the elderly. Strokes that cause unconsciousness or impair breathing or heart function are particularly serious. Functioning problems that continue after six months are most likely to be permanent, although some people continue to improve slowly. People who are younger and in better general health tend to recover faster and more completely.
Stroke symptoms need immediate medical attention. Quick action by a doctor can sometimes reduce the damage or prevent more damage. Many effects of a stroke require medical care such as oxygen or an intravenous line to provide the patient with fluids and nourishment.
For a stroke in evolution, anticoagulants such as heparin may be given. If the stroke is complete, these drugs are not effective.
If the stroke is caused by a blood clot, research suggests that paralysis and other symptoms may be prevented or reversed if clot-dissolving drugs such as streptokinase or tissue plasminogen activator are given within three hours of the stroke's onset. An examination must be done quickly to rule out the possibility of a hemorrhage, which can't be treated with clot-dissolving drugs.
Once a stroke is completed, some brain tissue is dead and its function can't be restored. However, removing blockages after a small stroke or transient ischemic attack in someone whose carotid artery is more than 70% blocked may reduce the risk of future strokes.
To reduce swelling and pressure on the brain in people with an acute stroke, drugs such as mannitol, or rarely, corticosteroids may be given. A person with a very severe stroke may be put on a respirator because of pneumonia or to maintain adequate breathing.
While dead brain tissue cannot be restored, intensive rehabilitation can help many people overcome disability by training other parts of the brain to do what the damaged part originally did. Rehabilitation usually begins quickly to keep the patient's muscles strong, to prevent muscular contractions and pressure sores and to teach the patient to walk and talk again. Rehabilitation may continue after a patient leaves the hospital.
