A stroke is the sudden destruction of brain cells when blood flow to the brain is disrupted, usually by a blockage in a blood vessel. It is a medical emergency that can cause weakness, speech problems, paralysis * , and death, although most people survive.
While eating lunch with her grandfather on a sunny afternoon, 14-year-old Carmen was in the midst of describing her summer camp plans when suddenly one side of her grandfather's face went slack. He tried to speak, but he was slurring his words. Without warning, he clutched the picnic table, and the drinking glass he held crashed to the ground.
“Grandma,” Carmen called. As her grandmother rushed to dial for emergency aid, Carmen held her grandfather's trembling hand.
A stroke occurs when the blood supply to part of the brain is suddenly interrupted, or when a blood vessel in the brain bursts, spilling blood into the spaces surrounding neurons (nerve cells). Like other cells, brain cells die when they no longer receive oxygen and nutrients from the bloodstream, or when they are damaged by sudden bleeding into or around the brain.
There are two major types of strokes. Ischemic strokes involve a reduced blood flow to the brain. Hemorrhagic (hem-o-RAJ-ik) strokes involve bleeding in the brain. Ischemia (is-KEY-me-a) is the term used to describe the loss of oxygen and nutrients when there is inadequate blood flow. If ischemia is left untreated, it can lead to infarction (in-FARK-shun), or cell and tissue death in the surrounding area.
Ischemic strokes occur when a blood vessel to the brain becomes blocked, suddenly decreasing or stopping blood flow and ultimately causing an infarction. Ischemic strokes account for approximately 87 percent of all strokes. A blood clot (also called a thrombus) is the most common cause of vessel blockage and brain infarction.
Blood clotting is necessary in the body to stop bleeding and allow repair of damaged areas, but when blood clots develop in the wrong place within an artery, they can cause injury by stopping the normal flow of blood. The chance of clots developing increases as people age.
An embolus (EM-bowl-us) is a clot that has formed in a blood vessel somewhere in the body, often in the heart. It can break away from the wall of the vessel where it was formed, travel through the circulatory system, and become wedged in the brain, causing an embolic stroke. Ischemic strokes also can be caused by the formation of a blood clot in one of the cerebral arteries (arteries supplying blood to the brain). If the clot grows large enough, it will block blood flow.
Stenosis (ste-NO-sis), or a narrowing of the arteries, also can cause ischemia. Occurring in large arteries or small arteries, stenosis is called blood vessel disease or small vessel disease. The most common blood vessel disease that causes stenosis is atherosclerosis (ath-ER-ohskler-OH-sis). Deposits of plaque (a mixture of cholesterol and other fatty substances) build up along the inner walls of larger and medium-sized arteries, causing thickening, hardening, and loss of elasticity of the artery walls. Small pieces of plaque can break off from the blood vessel walls and form a clot.
Some people get a warning that they may be headed for a future stroke. A transient ischemic attack (TIA) is a very small stroke caused by a temporarily blocked blood vessel. Unlike a full stroke, a TIA leaves no permanent damage. Symptoms are similar to those of a full stroke, but they usually last 24 hours or less. It is impossible to know whether the symptoms are caused by a stroke or by a TIA, so any symptoms should receive immediate medical attention. Having a TIA increases the risk of having a full stroke in the future, and medical attention can sometimes prevent or lessen the severity of the stroke.
Hemorrhagic strokes are caused by burst blood vessels. In a healthy brain, the neurons do not come into direct contact with blood. Oxygen and nutrients move across a membrane from the blood vessel to the brain cells. Neuroglial (noo-ro-GLEE-al) cells help control which fluids and nutrients reach the neurons of the brain. When an artery in the brain bursts, blood spills out into the surrounding tissue, overriding the control of neuroglial cells and disrupting the delicate chemical balance of the brain.
Hemorrhagic strokes may occur in several ways. Aneurysms, or weak spots on artery walls, can stretch or “balloon” until eventually they break and spill blood into surrounding brain cells. Hemorrhages can also happen when plaque-encrusted arteries lose their elasticity and become brittle and thin enough to crack. Hypertension (high blood pressure) increases the risk that a brittle artery wall will give way and release blood into surrounding brain tissue.
Individuals who have an arteriovenous (ar-TEER-ee-o-VEN-us) malformation (a tangle of defective blood vessels and capillaries within the brain that can rupture) can also be at increased risk of hemorrhagic stroke. Although hemorrhagic strokes are less common than ischemic strokes, they have a much higher fatality rate because more brain tissue can be damaged more quickly.
Symptoms of stroke, such as those experienced by Carmen's grandfather, appear suddenly. They may include:
Strokes are medical emergencies and require immediate medical attention.
Doctors have diagnostic techniques and imaging tools to help diagnose strokes quickly and accurately. When a person with signs and symptoms of stroke arrives at the hospital, the first diagnostic step is a physical examination and a medical history. Often, an electrocardiogram * and a CT scan *
Imaging tests also help healthcare professionals to evaluate stroke. The CT scan may rule out a hemorrhage or may show evidence of early infarction. If the stroke is caused by a hemorrhage, a CT scan can reveal any bleeding into the brain. CT scans and other early steps are critical in determining the cause of the stroke and emergency treatment. MRIs * may be taken to detect subtler changes in brain tissue or areas of dead tissue soon after a stroke.
Stroke treatment varies depending on the whether the stroke is hemorrhagic or ischemic. Treatment most often involves medication and rehabilitation. Acute stroke therapy uses medication to stop a stroke while it is happening by either quickly dissolving the blood clot that is causing the stroke or by stopping the bleeding of a hemorrhagic stroke. Surgery is almost never used for acute stroke treatment. Very rarely, and only in hemorrhagic stroke, a neurosurgeon may consider placing a drain into an area of the brain to remove some blood and relieve pressure on the brain. Carotid endarterectomy (kar-OT-id en-DAR-ta-rek-to-ME) (surgery to remove plaque buildup in carotid arteries) may be indicated to prevent an ischemic stroke from happening, although it is rarely performed as an emergency procedure.
Various medications can be used to treat stroke:
Surgery is not used to treat an ischemic stroke, but it is sometimes used to treat a hemorrhagic stroke. An attempt to surgically remove accumulated blood and intracranial pressure caused by a hemorrhagic stroke is a delicate procedure, as the surgery itself may generate additional bleeding, thereby causing more harm. Surgery is sometimes used to repair aneurysms or vascular malformations in and around the brain.
Post-stroke rehabilitation helps people overcome the disabilities that result from stroke damage. For some people, such as Carmen's grandfather, acute stroke treatment and poststroke therapy lead to a full recovery. For others, recovery is only partial.
Although strokes occur in the brain, they may affect the entire body and all activities of daily living. Some of the disabilities that may result from a stroke include paralysis (or partial paralysis) of different parts of the body, difficulties with memory and concentration, speech problems, and emotional distress as people cope with their changed circumstances. Rehabilitation may involve several different forms of therapy:
Psychotherapy often is useful following a stroke because depression, anxiety, frustration, and anger are common poststroke symptoms.
The most important risk factors * for stroke are hypertension (high blood pressure), heart disease, diabetes, and smoking. Others factors that increase the risk of having a stroke are heavy alcohol consumption, high cholesterol levels, and genetic or congenital conditions, such as vascular (blood vessel) abnormalities.
People with hypertension (high blood pressure) have a risk of stroke that is four to six times greater than those without hypertension. One-third of adults in the United States have high blood pressure. Antihypertensive drugs and attention to diet can decrease a person's risk of stroke.
After hypertension, the second most powerful risk factor for stroke is heart disease, particularly the condition known as atrial fibrillation * Diabetes
People with diabetes have three times the risk of stroke as those without diabetes. The relative risk is highest in the fifth and sixth decades of life and decreases after that. People with diabetes who control their blood sugar level well, who avoid smoking, and who avoid or control hypertension are less likely to have strokes.
Smokers have a 40 to 60 percent greater chance of having a stroke than nonsmokers. Smoking increases a person's chance of ischemic stroke, independent of all other risk factors.
High cholesterol levels can contribute to the risk of stroke. Too much cholesterol in the blood is associated with plaque developing in the walls of arteries (atherosclerosis), leading to stenosis of blood vessels. By lowering cholesterol through diet and exercise, a person can lower the risk of atherosclerosis and stroke. Doctors may prescribe cholesterol-lowering medication for people with high cholesterol levels.
Many strokes can be prevented with changes in lifestyle. These changes include:
To prevent stroke, doctors may prescribe medications to lower blood pressure and cholesterol levels. In some cases, particularly if a person has atrial fibrillation, doctors may prescribe regular doses of aspirin, Coumadin (an anticoagulant medication that stops the formation of clots), or other medications that prevent blood clotting. If carotid (ka-ROT-id) arteries (arteries supplying the brain) are partially blocked by plaque, surgery can clear them and prevent strokes in many cases.
Strokes can happen to people of either sex no matter what their age or racial background. Transient ischemic attacks (TIAs) multiply a person's risk of having a full stroke and should receive immediate medical attention.
See also Aging • Alcoholism • Aneurysm • Diabetes • Embolism • Genetic Disease: Overview • Heart Disease: Overview • Hypertension • Tobacco-Related Diseases: Overview • Vascular Diseases: Overview
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* paralysis (pah-RAH-luh-sis) is the loss or impairment of the ability to move some part of the body.
* ischemia (is-KEY-me-a) is the loss of oxygen and nutrients when there is inadequate blood flow to an organ or tissue.
* infarction (in-FARK-shun) is cell and tissue death resulting from oxygen deprivation caused by blockage of the tissue's blood supply.
* electrocardiogram (e-lek-tro-KAR-dee-o-gram), also known as an EKG, is a test that records and displays the electrical activity of the heart.
* CT scans are the shortened name for computed tomography (to-MOG-ra-fee), which uses computers to view structures inside the body. Formerly called computerized axial tomography (CAT).
* MRI, which is short for magnetic resonance imaging, produces computerized images of internal body tissues based on the magnetic properties of atoms within the body.
* risk factors are any factors that increase the chance of developing a disease.
* atrial fibrillation (AY-tree-al fib-ri-LAY-shun) is the arrhythmic or irregular beating of the left upper chamber of the heart. This irregular heartbeat leads to an irregular flow of blood and to the formation of blood clots that can leave the heart and travel to the brain, causing a stroke.