A stroke is a "brain attack," caused either by bleeding in the brain or a loss of blood flow to the brain. The brain cells die from a lack of food and oxygen, or from damage from being surrounded by blood. Immediate treatment is essential.
There are two major kinds of stroke: ischemic stroke and hemorrhagic stoke. Ischemic stroke happens when a blood vessel supplying the brain is blocked. 80% of strokes are this kind.
Ischemic stroke can happen three ways.
- In embolic stroke, a blood clot forms somewhere else in the body and travels through the blood vessels until it gets stuck in the brain, blocking off a blood vessel.
- In thrombotic stroke, a blood clot forms in one of the arteries in the brain, and grows and grows until it is large enough to block blood flow.
- In stenosis, the artery gets narrower and narrower as plaque (a mixture of fatty substances, including cholesterol and other lipids) and blood clots build up along the artery wall.
Hemorrhagic stroke happens when there is bleeding into or around the brain. Twenty percent of strokes are this kind. Normally the neurons never touch the blood directly; they get the food and nutrients they need across a thin membrane. When the brain bleeds, the blood surrounds the neurons and keeps them from working. The bleeding also means the blood isn’t going where it should, so some brain cells starve. Hemorrhagic stroke can happen two ways. A weak spot in an artery wall, or aneurysm, can balloon out and break, spilling blood. Or arteries full of plaque can get brittle and break. High blood pressure increases the chances that a hardened artery will break and cause a stroke.
The first step in diagnosis is a short neurological examination. The doctor will ask the patient or a companion what happened and when the symptoms began. Blood tests, an electroencephalogram, and CT scans will often be done. The doctor measures the damage done by the stroke by asking the patient to answer questions and to perform several physical and mental tests.
Fifty thousand Americans have a mini-ischemic stroke every year. No permanent damage occurs and symptoms usually subside within an hour. About 95% of people who have mini-ischemic strokes experience a stroke within a month of the attack. If it occurs at the part of the brain that controls vision, visual damage may occur. When oxygen to the eye is reduced, vision decreases like a curtain closing over the eye. Mini-ischemic stroke patients may develop poor night vision, which signals blocked arteries.
Recurrent stroke is frequent; about 25 percent of people who recover from their first stroke will have another stroke within 5 years. Recurrent stroke is a major contributor to stroke disability and death, with the risk of severe disability or death from stroke increasing with each stroke recurrence. The risk of a recurrent stroke is greatest right after a stroke, with the risk decreasing with time. About 3 percent of stroke patients will have another stroke within 30 days of their first stroke and one-third of recurrent strokes take place within 2 years of the first stroke.