Ischemic stroke occurs when a blood vessel carrying blood to the brain is blocked by a blood clot. This causes blood not to reach the brain. High blood pressure is the most important risk factor for this type of stroke. Ischemic strokes account for about 87% of all strokes. An ischemic stroke can occur in two ways.
In an embolic stroke, a blood clot or plaque fragment forms somewhere in the body (usually the heart) and travels to the brain. Once in the brain, the clot travels to a blood vessel small enough to block its passage. The clot lodges there, blocking the blood vessel and causing a stroke. About 15% of embolic strokes occur in people with atrial fibrillation (Afib). The medical word for this type of blood clot is embolus.
A thrombotic stroke is caused by a blood clot that forms inside one of the arteries supplying blood to the brain. This type of stroke is usually seen in people with high cholesterol levels and atherosclerosis. The medical word for a clot that forms on a blood-vessel deposit is thrombus.
Two types of blood clots can cause thrombotic stroke: large vessel thrombosis and small vessel disease.
Large Vessel Thrombosis
The most common form of thrombotic stroke (large vessel thrombosis) occurs in the brain’s larger arteries. In most cases it is caused by long-term atherosclerosis in combination with rapid blood clot formation. High cholesterol is a common risk factor for this type of stroke.
Small Vessel Disease
Another form of thrombotic stroke happens when blood flow is blocked to a very small arterial vessel (small vessel disease or lacunar infarction). Little is known about the causes of this type of stroke, but it is closely linked to high blood pressure.