What is a Stroke?
A stroke is a sudden interruption in the blood supply of the brain. Most strokes are caused by an abrupt blockage of arteries leading to the brain (ischemic stroke). Other strokes are caused by bleeding into brain tissue when a blood vessel bursts (hemorrhagic stroke). Strokes are often referred to as a brain attack because theyoccur rapidly and require immediate medical treatment.
Blood is carried to the brain via a complex network of arteries and vessels. A stroke occurs when one of these arteries becomes blocked or an artery ruptures.
The effects of a stroke depend on which part of the brain is injured, and how severely it is injured. Strokes may cause sudden weakness, loss of sensation or difficulty with speaking, seeing or walking. Since different parts of the brain control different areas and functions, it is usually the area immediately surrounding the stroke that is affected.
Types of Stroke
There are several types of stroke, and each type has different causes. The three main types of stroke are listed below.
The most common type of stroke -- accounting for almost 80 percent of all strokes -- is caused by a clot or other blockage within an artery leading to the brain. Ischemic stroke can be caused by several different kinds of diseases. If the arteries become too narrow, blood cells may collect and form blood clots. These blood clots can block the artery where they are formed (thrombosis), or can dislodge and become trapped in arteries closer to the brain (embolism). Another cause of stroke is blood clots in the heart, which can occur as a result of irregular heartbeat (for example, atrial fibrillation), heart attack, or abnormalities of the heart valves. While these are the most common causes of ischemic stroke, there are many other possible causes. Examples include use of street drugs, traumatic injury to the blood vessels of the neck or disorders of blood clotting.
An intracerebral hemorrhage is a type of stroke caused by the sudden rupture of an artery within the brain. Blood is then released into the brain, compressing brain structures. The most common cause of intracerebral hemorrhage is high blood pressure (hypertension). Since high blood pressure by itself often causes no symptoms, many people with intracranial hemorrhage are not aware that they have high blood pressure, or that it needs to be treated. Less common causes of intracerebral hemorrhage include trauma, infections, tumors, blood clotting deficiencies and abnormalities in blood vessels.
A subarachnoid hemorrhage is also a type of stroke caused by the sudden rupture of an artery. A subarachnoid hemorrhage differs from an intracerebral hemorrhage in that the location of the rupture leads to blood filling the space surrounding the brain rather than inside of it. Subarachnoid hemorrhage is most often caused by abnormalities of the arteries at the base of the brain, called cerebral aneurysms. These are small areas of rounded or irregular swellings in the arteries. Where the swelling is most severe, the blood vessel wall become weak and prone to rupture.