What is a Stroke?

A stroke is a sudden interruption of the blood supply to the brain. There are two major kinds of stroke, ischemic (i-skee-mik) stroke and hemorrhagic (hem-er-ah-jik) stroke. There is also a transient ischemic attack (TIA) sometimes known as “mini stroke.”

Ischemic stroke
In an ischemic stroke, a blood vessel in the brain becomes blocked, most commonly by an obstructive blood clot. Clot may form in the blood vessel or travel from somewhere else in the bloodstream, often from other arteries or the heart. Atherosclerosis, the buildup of fatty plaque on artery walls, represents another common cause of stroke. Plaque buildup can narrow arteries, ultimately causing or contributing to stroke. Ischemic stroke stops oxygen and nutrients from getting to the brain. Brain cells begin to die within minutes, but swelling and inflammation in the area of the stroke may continue for days. About 80% of all strokes are ischemic strokes.

The area of the brain immediately downstream of a blocked artery (the “core” of a stroke) is often irreversibly damaged. The area slightly more distant from the blockage (the “penumbra”) represents tissue at risk. Treatment for ischemic stroke works to restore blood flow to the brain. Time is critical--the longer blood flow restoration is delayed, the more cells may die. If less than 4 1/2 hours have passed since symptoms began, doctors may use a medication that dissolves blood clots.

Hemorrhagic stroke
In a hemorrhagic stroke, a blood vessel bursts causing bleeding into or around the brain. Certain things make hemorrhagic stroke more likely: common conditions such as hypertension; rarer conditions affecting the blood vessel structure and stability (e.g. cerebral amyloid angiopathy, arteriovenous malformations, and some genetic diseases); and decreased blood clotting capacity because of disease or medication.

Hemorrhagic stroke may carry many names, depending on the location of the bleeding. It may be referred to as an intracraniall hemorrhage (a global term); an intracerebral hemorrhage (hemorrhage into the brain substance itself); or hemorrhage into one of the spaces within or surrounding brain (for example, a subarachnoid hemorrhage).

Hemorrhagic stroke is less common but more deadly than ischemic stroke.

Treatment for hemorrhagic stroke is more difficult. Surgery or other treatments to stop bleeding or reduce pressure in the brain may be an option. Medicines may be used to control blood pressure, brain swelling and other problems.

Transient Ischemic Attack (“mini stroke”)
Symptoms of a TIA are similar to the symptoms of a stroke, but they are much shorter-lived (less than one hour in most cases,) and always less than 24 hours) TIAs usually don't cause damage, but they can be a serious warning sign of stroke. Following a TIA, the risk of stroke within 90 days is estimated to be 10-20%. Receiving early treatment for a TIA, including analysis of stroke risk factors and implementation of changes to reduce risk may help prevent a stroke.

Stroke risks