What Is a Stroke?
Types of strokes
A stroke occurs when blood flow to the brain is interrupted, either by a clot or a rupture in a blood vessel. When the part of the brain that’s deprived of blood can no longer get the oxygen and other nutrients it needs, it begins to die.
There are two types of stroke:
- Ischemic strokes occur when a clot blocks a blood vessel to the brain. If blood flow is blocked only temporarily, it results in a transient ischemic attack (TIA), also known as a ministroke.
- Hemorrhagic strokes occur when a blood vessel ruptures, causing blood to leak into the brain.
Ischemic strokes, which account for more than 80 percent of all strokes, occur when a clot obstructs a blood vessel that supplies blood to the brain. Ischemic strokes usually result from atherosclerosis, a condition in which fatty deposits develop on the walls of blood vessels. There are two ways in which atherosclerosis can cause an ischemic stroke:
- In cerebral thrombosis, a blood clot develops right at the clogged part of the vessel.
- In a cerebral embolism, a blood clot forms in another location, usually the heart or large arteries of the chest and neck. If part of the clot breaks loose, it will travel through the bloodstream until it reaches a blood vessel that's too small to allow its passage. When this occurs in the brain, the result is a stroke.
Ischemic strokes can also result from atrial fibrillation, a condition in which the upper chambers of the heart beat rapidly and irregularly, causing blood to pool and clot. If one of these clots breaks loose, it can result in a stroke.
Transient ischemic attacks
Sometimes called ministrokes, transient ischemic attacks (TIAs) are warning signs that an ischemic stroke may be looming on the horizon. In a TIA, the blockage of blood flow to the brain is only temporary, so symptoms disappear after a short time. But since TIAs are often precursors of a major stroke, they should be taken just as seriously.
In a hemorrhagic stroke, a blood vessel actually ruptures and bleeds into the brain. This can occur in two ways:
- In an intracerebral hemorrhage, a ruptured blood vessel bleeds directly into the brain tissue. As blood pools in the brain, it compresses the surrounding brain tissue and may also cause a sudden increase in pressure within the brain. The affected brain cells can be damaged and may begin to die.
- A subarachnoid hemorrhage occurs when a blood vessel outside of the brain ruptures, filling the subarachnoid space (the area of skull surrounding the brain) with blood. This causes a sudden increase in pressure around the brain, which may result in rapid loss of consciousness or death.
Hemorrhagic strokes usually occur when a blood vessel is already weakened in one of two ways:
- In an aneurysm, a weakened region of a blood vessel stretches out like a balloon. If left untreated, the ballooning vessel may continue to stretch until it bursts.
- An arteriovenous malformation (AVM) is a cluster of abnormally formed blood vessels. Although AVMs don't always cause problems, these vessels are more likely to rupture.