An ischemic stroke occurs when a blood vessel that supplies the brain becomes blocked. This affects blood flow to part of the brain. The brain cells and tissues start to die within minutes from lack of oxygen and nutrients. Ischemic strokes are further divided into two groups:
Thrombotic strokes. These are caused by a blood clot that develops in the blood vessels inside the brain.
Embolic strokes. These are caused by a blood clot that develops elsewhere in the body. The clot then travels to one of the blood vessels in the brain through the bloodstream.
Thrombotic strokes are strokes caused by a blood clot (thrombus) that develops in the arteries supplying blood to the brain. This type of stroke is usually seen in older people, especially those with high cholesterol and a buildup of fat and lipids inside the walls of blood vessels (atherosclerosis) or diabetes.
Sometimes, symptoms of a thrombotic stroke can occur suddenly. They can happen during sleep or in the early morning. At other times, it may occur gradually over a period of hours or even days.
Mini-strokes are also called transient ischemic attacks (TIAs) One of more of these may happen before a thrombotic stroke. TIAs may last for a few minutes or up to 24 hours. They are often a warning sign that a stroke may occur. Symptoms of a TIA are often mild and temporary, but they are similar to those caused by a stroke.
Another type of stroke that occurs in the small blood vessels in the brain is called a lacunar infarct. The word lacunar comes from the Latin word meaning "hole" or "cavity." Lacunar infarctions are often found in people who have diabetes or high blood pressure.
Embolic strokes are usually caused by a blood clot that forms elsewhere in the body (embolus) and travels through the bloodstream to the brain. Embolic strokes are often caused by heart disease or heart surgery. They happen quickly and without any warning signs. About 3 in 20 embolic strokes occur in people with atrial fibrillation. This is a type of heart rhythm problem where the upper chambers of the heart (atria) don't beat well.