An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery.
An ischemic stroke typically results from blockage of an artery that supplies the brain, most commonly a branch of one of the internal carotid arteries (Fig. 1: Supplying the Brain with Blood).
Commonly, blockages are blood clots (thrombi) or pieces of fatty deposits (atheromas, or plaques) due to atherosclerosis. Such blockages often occur in the following ways:
Several conditions besides rupture of an atheroma can trigger or promote the formation of blood clots, increasing the risk of blockage by a blood clot. They include the following:
Blood clots in a brain artery do not always cause a stroke. If the clot breaks up spontaneously within less than 15 to 30 minutes, brain cells do not die and people's symptoms resolve. Such cases are called a transient ischemic attack (TIA—see Transient Ischemic Attacks).
If an artery narrows very gradually, other arteries (called collateral arteries—Fig. 1: Supplying the Brain with Blood) sometimes enlarge to supply blood to the parts of the brain normally supplied by the clogged artery. Thus, if a clot occurs in an artery that has developed collateral arteries, people may not have symptoms.
|Clogs and Clots: Causes of Ischemic Stroke
When an artery that carries blood to the brain becomes clogged or blocked, an ischemic stroke can occur. Arteries may be blocked by fatty deposits (atheromas, or plaques) due to atherosclerosis. Arteries in the neck, particularly the internal carotid arteries, are a common site for atheromas.
Arteries may also be blocked by a blood clot (thrombus). Blood clots may form on an atheroma in an artery. Clots may also form in the heart of people with a heart disorder. Part of a clot may break off and travel through the bloodstream (becoming an embolus). It may then block an artery that supplies blood to the brain, such as one of the cerebral arteries.
Lacunar infarction is another cause of ischemic stroke. In lacunar infarction, one of the small arteries deep in the brain becomes blocked when part of its wall deteriorates and is replaced by a mixture of fat and connective tissue—a disorder called lipohyalinosis. Lipohyalinosis is different from atherosclerosis, but both disorders can cause arteries to be blocked. Lacunar infarction tends to occur in older people with diabetes or poorly controlled high blood pressure. Only a small part of the brain is damaged in lacunar infarction, and the prognosis is usually good. However, over time, many small lacunar infarcts often develop.
An ischemic stroke can also result from any disorder that reduces the amount of blood supplied to the brain. For example, an ischemic stroke can occur if inflammation of blood vessels (vasculitis) or infection (such as herpes simplex) narrows blood vessels that supply the brain. Migraine headaches or drugs such as cocaine and amphetamines can cause spasm of the arteries, which can narrow the arteries supplying the brain long enough to cause a stroke. Rarely, a stroke results from a general decrease in blood flow, as occurs when people lose a lot of blood or have very low blood pressure.
Occasionally, an ischemic stroke occurs when blood flow to the brain is normal but the blood does not contain enough oxygen. Disorders that reduce the oxygen content of blood include a severe deficiency of red blood cells (anemia), suffocation, and carbon monoxide poisoning. Usually, brain damage in such cases is widespread (diffuse), and coma results.
Sometimes a blood clot in a leg vein (see Deep Vein Thrombosis (DVT)) or, rarely, small pieces of fat from the marrow of a broken leg bone move into the bloodstream. Usually, these blood clots and pieces of fat travel to the heart and block an artery in the lungs (see Pulmonary Embolism (PE)). However, some people have an abnormal opening between the right and left upper chambers of the heart (called a patent foramen ovale). In such people, the blood clots and pieces of fat may go through the opening and thus bypass the lungs and enter the aorta (the largest artery in the body). If they travel to arteries in the brain, a stroke can result.
The major risk factors for ischemic stroke are
Other risk factors include
Usually, symptoms occur suddenly and are often most severe a few minutes after they start because most ischemic strokes begin suddenly, develop rapidly, and cause death of brain tissue within minutes to hours. Then, most strokes become stable, causing little or no further damage. Strokes that remain stable for 2 to 3 days are called completed strokes. Sudden blockage by an embolus is most likely to cause this kind of stroke.
Less commonly, symptoms develop slowly. They result from strokes that continue to worsen for several hours to a day or two, as a steadily enlarging area of brain tissue dies. Such strokes are called evolving strokes. The progression of symptoms and damage is usually interrupted by somewhat stable periods. During these periods, the area temporarily stops enlarging or some improvement occurs. Such strokes are usually due to the formation of clots in a narrowed artery.
Many different symptoms can occur, depending on which artery is blocked and thus which part of the brain is deprived of blood and oxygen (see Brain Dysfunction by Location). When the arteries that branch from the internal carotid artery (which carry blood along the front of the neck to the brain) are affected, the following are most common:
When the arteries that branch from the vertebral arteries (which carry blood along the back of the neck to the brain) are affected, the following are most common:
Many other symptoms, such as difficulty speaking (for example, slurred speech), impaired consciousness (such as confusion), loss of coordination, and urinary incontinence, can occur.
Severe strokes may lead to stupor or coma. In addition, strokes, even milder ones, can cause depression or an inability to control emotions. For example, people may cry or laugh inappropriately.
Some people have a seizure when the stroke begins. Seizures may also occur months to years later. Late seizures result from scarring or materials that are deposited from blood in the damaged brain tissue.
Occasionally, fever develops. It may be caused by the stroke or another disorder.
If symptoms, particularly impaired consciousness, worsen during the first 2 to 3 days, the cause is often swelling due to excess fluid (edema) in the brain. Symptoms usually lessen within a few days, as the fluid is absorbed. Nonetheless, the swelling is particularly dangerous because the skull does not expand. The resulting increase in pressure can cause the brain to shift, further impairing brain function, even if the area directly damaged by the stroke does not enlarge. If the pressure becomes very high, the brain may be forced downward in the skull, through the rigid structures that separate the brain into compartments. The resulting disorder is called herniation (Fig. 1: Herniation: The Brain Under Pressure).
Strokes can lead to other problems. If swallowing is difficult, people may not eat enough and become malnourished. Food, saliva, or vomit may be inhaled (aspirated) into the lungs, resulting in aspiration pneumonia. Being in one position too long can result in pressure sores and lead to muscle loss. Not being able to move the legs can result in the formation of blood clots in deep veins of the legs and groin (deep vein thrombosis). Clots can break off, travel through the bloodstream, and block an artery to a lung (a disorder called pulmonary embolism). People may have difficulty sleeping. The losses and problems resulting from the stroke may make people depressed.
Doctors can usually diagnose an ischemic stroke based on the history of events and results of a physical examination. Doctors can usually identify which artery in the brain is blocked based on symptoms (Fig. 1: When Specific Areas of the Brain Are Damaged). For example, weakness or paralysis of the left leg suggests blockage of the artery supplying the area on the right side of the brain that controls the left leg's muscle movements.
Computed tomography (CT) is usually done first. CT helps distinguish an ischemic stroke from a hemorrhagic stroke, a brain tumor, an abscess, and other structural abnormalities. Doctors also measure the blood sugar level to rule out a low blood sugar level (hypoglycemia), which can cause similar symptoms. If available, diffusion-weighted magnetic resonance imaging (MRI), which can detect ischemic strokes within minutes of their start, may be done next.
Identifying the precise cause of the stroke is important. If the blockage is a blood clot, another stroke may occur unless the underlying disorder is corrected. For example, if blood clots result from an abnormal heart rhythm, treating that disorder can prevent new clots from forming and causing another stroke.
Tests for causes may include the following:
Imaging tests enable doctors to determine how narrowed the carotid arteries are and thus to estimate the risk of a subsequent stroke or TIA. Such information helps determine which treatments are needed.
For cerebral angiography, a thin, flexible tube (catheter) is inserted into an artery, usually in the groin, and threaded through the aorta to an artery in the neck (see Angiography). Then, a dye is injected to outline the artery. Thus, this test is more invasive than other tests that provide images of the brain's blood supply. However, it provides more information. Cerebral angiography may be done before atheromas are removed surgically or when vasculitis is suspected.
Rarely, a spinal tap (lumbar puncture) is done—for example, after CT, when doctors still need to determine whether strokelike symptoms are due to an infection or whether a subarachnoid hemorrhage is present (see Subarachnoid Hemorrhage). This procedure is done only if doctors think that the brain is not under excess pressure (usually determined by CT or MRI).
About 10% of people who have an ischemic stroke recover almost all normal function, and about 25% recover most of it. About 40% of people have moderate to severe impairments requiring special care, and about 10% require care in a nursing home or other long-term care facility. Some people are physically and mentally devastated and unable to move, speak, or eat normally. About 20% of people who have a stroke die in the hospital. The proportion is higher among older people. About 25% of people who recover from a stroke have another stroke within 5 years. Subsequent strokes impair function further.
During the first few days after an ischemic stroke, doctors usually cannot predict whether a person will improve or worsen. Younger people and people who start improving quickly are likely to recover more fully. About 50% of people with one-sided paralysis and most of those with less severe symptoms recover some function by the time they leave the hospital, and they can eventually take care of their basic needs. They can think clearly and walk adequately, although use of the affected arm or leg may be limited. Use of an arm is more often limited than use of a leg. Most impairments still present after 12 months are permanent.
People who have any symptom suggesting an ischemic stroke should go to an emergency department immediately. The earlier the treatment, the better are the chances for recovery.
The first priority is to restore the person's breathing, heart rate, blood pressure (if low), and temperature to normal. An intravenous line is inserted to provide drugs and fluids when needed. If the person has a fever, it may be lowered using acetaminophen, ibuprofen, or a cooling blanket because brain damage is worse when body temperature is elevated. Generally, doctors do not immediately treat high blood pressure unless it is very high (over 220/120 mm Hg) because when arteries are narrowed, blood pressure must be higher than normal to push enough blood through them to the brain. However, very high blood pressure can injure the heart, kidneys, and eyes and must be lowered.
If a stroke is very severe, drugs such as mannitol may be given to reduce swelling and the increased pressure in the brain. Some people need a ventilator to breathe adequately.
Specific treatment of stroke may include drugs to break up blood clots (thrombolytic drugs) and drugs to make blood less likely to clot (antiplatelet drugs and anticoagulants), followed by rehabilitation. At some specialized centers, blood clots are physically removed from arteries (called mechanical thrombectomy).
Measures to prevent another stroke include control of risk factors (including high blood pressure, diabetes, and high cholesterol levels), use of drugs that make blood less likely to clot, and sometimes surgery or angioplasty to open blocked arteries.
Thrombolytic (fibrinolytic) drugs:
In certain circumstances, a drug called tissue plasminogen activator (tPA) is given intravenously to break up clots and help restore blood flow to the brain. Because tPA can cause bleeding in the brain and elsewhere, it usually should not be given to people with certain conditions, such as the following:
Before tPA is given, CT is done to rule out bleeding in the brain. To be effective and safe, tPA, given intravenously, must be started within 3 hours of the beginning of an ischemic stroke. Some experts recommend using tPA up to 4.5 hours after an ischemic stroke begins. But when tPA is given between 3 and 4.5 hours, additional conditions prohibit its use. These conditions include being over age 80, having a severe stroke, and having a history of both stroke and diabetes mellitus. After 4.5 hours, most of the damage to the brain cannot be reversed, and the risk of bleeding outweighs the possible benefit of using tPA.
Pinpointing when the stroke began may be difficult. So doctors assume that the stroke began the last time a person was known to be well. For example, if a person awakens with symptoms of a stroke, doctors assume the stroke began when the person was last seen awake and well. Thus, tPA can be used in only a few people who have had a stroke.
If people arrive at the hospital 3 to 6 hours (occasionally, up to 18 hours) after the stroke began, they may be given tPA or another thrombolytic drug. But the drug must be given through a catheter placed directly in the blocked artery rather than intravenously. For this treatment (called thrombolysis-in-situ), doctors make an incision in the skin, usually in the groin, and insert a catheter into an artery. The catheter is then threaded through the aorta and other arteries, to the clot. The clot is partly broken up with the catheter wire and then injected with tPA. This treatment is usually available only at specialized stroke centers.
For this procedure, doctors use a device to physically remove the blood clot. This procedure is often done when people have had a severe stroke and have been ineffectively treated with tPA, given intravenously or by catheter. This procedure must be done within 8 hours of when symptoms began. Different types of devices can be used. For example, a tiny corkscrew-shaped device can be attached to a catheter, which is inserted through an incision, often in the groin, and threaded to the clot. The clot is then drawn out through the catheter. Mechanical thrombectomy may be useful for people who cannot be given tPA but is still usually considered experimental.
Antiplatelet drugs and anticoagulants:
If a thrombolytic drug cannot be used, most people are given aspirin (an antiplatelet drug) as soon as they get to the hospital. If symptoms seem to be worsening, anticoagulants such as heparin are occasionally used, but their effectiveness has not been proved. Antiplatelet drugs make platelets less likely to clump and form clots. (Platelets are tiny cell-like particles in the blood that help it clot in response to damaged blood vessels.) Anticoagulants inhibit proteins in blood that help it to clot (clotting factors).
Regardless of the initial treatment, long-term treatment usually consists of aspirin or another antiplatelet drug to reduce the risk of blood clots and thus of subsequent strokes (see Prevention). People who have atrial fibrillation or a heart valve disorder are given anticoagulants (such as warfarin) instead of antiplatelet drugs, which do not seem to prevent blood clots from forming in the heart. Dabigatran, apixaban, and rivaroxaban are new anticoagulants that are sometimes used instead of warfarin. Occasionally, people at high risk of another stroke are given both aspirin and an anticoagulant.
If people have been given a thrombolytic drug, doctors usually wait at least 24 hours before antiplatelet drugs or anticoagulants are started because these drugs add to the already increased risk of bleeding in the brain. Anticoagulants are not given to people who have uncontrolled high blood pressure or who have had a hemorrhagic stroke.
Once an ischemic stroke is completed, surgical removal of atheromas or clots (endarterectomy) in an internal carotid artery may be done. Carotid endarterectomy can help if all of the following are present:
In such people, carotid endarterectomy may reduce the risk of subsequent strokes. It also reestablishes the blood supply to the affected area, but it cannot restore lost function because some brain tissue is dead.
For carotid endarterectomy, a general anesthetic is used. The surgeon makes an incision in the neck over the area of the artery that contains the blockage and an incision in the artery. The blockage is removed, and the incisions are closed. For a few days afterwards, the neck may hurt, and swallowing may be difficult. Most people can stay in the hospital 1 or 2 days. Heavy lifting should be avoided for about 3 weeks. After several weeks, people can resume their usual activities.
Carotid endarterectomy can trigger a stroke because the operation may dislodge clots or other material that can then travel through the bloodstream and block an artery. However, after the operation, the risk of stroke is lower for several years than it is when drugs are used.
In other narrowed arteries, such as the vertebral arteries, endarterectomy is typically not done because it is riskier when it is done in arteries other than the internal carotid arteries.
People should find a surgeon who is experienced doing this operation and who has a low rate of serious complications (such as heart attack, stroke, and death) after the operation. If people cannot find such a surgeon, the risks of endarterectomy outweigh its expected benefits.
If endarterectomy is too risky, a less invasive procedure can be done: A wire mesh tube (stent) with an umbrella filter may be placed in the carotid artery. The stent helps keep the artery open, and the filter catches blood clots and prevents them from reaching the brain and causing a stroke. The filter is similar to one used to prevent pulmonary embolism (Fig. 3: Umbrellas: One Way to Prevent Pulmonary Embolism). After a local anesthetic is given, a catheter is inserted through a small incision into a large artery near the groin or in the arm and is threaded to the internal carotid artery in the neck. A dye that can be seen on x-rays (radiopaque dye) is injected, and x-rays are taken so that the narrowed area can be located. After the stent and filter are placed, the catheter is removed. People remain awake for the procedure, which usually takes 1 to 2 hours. The procedure appears to be as safe as endarterectomy and as effective in preventing strokes and death.
Statins are drugs that lower levels of cholesterol and other fats (lipids). They are often given when strokes result from the buildup of fatty deposits in an artery. Such therapy can help prevent strokes from recurring.
Treatment of problems due to strokes:
Measures to prevent aspiration pneumonia (see Aspiration Pneumonia) and pressure sores (see Prevention) are started early. Heparin, injected under the skin, may be given to help prevent deep vein thrombosis (see Prevention). People are closely monitored to determine whether the esophagus, bladder, and intestines are functioning. Often, other disorders such as heart failure, abnormal heart rhythms, and lung infections must be treated. High blood pressure is often treated after the stroke has been stabilized.
Because a stroke often causes mood changes, especially depression, family members or friends should inform the doctor if the person seems depressed. Depression can be treated with drug therapy and psychotherapy (see Treatment).
Last full review/revision March 2014 by Elias A. Giraldo, MD, MS