An ischemic stroke occurs when an artery in the brain becomes blocked or clogged, cutting off the blood flow to a portion of the brain.
There are two types of ischemic stroke:
A thrombotic stroke occurs when an artery in the brain narrows, allowing a blood clot to clog the artery and cut off blood flow. This is the most common kind of stroke. Signs usually appear suddenly and increase over hours. Thrombotic strokes often happen at night or the first thing in the morning.
An embolic stroke is caused by a blood clot that breaks free from an artery or from the heart and flows through the blood stream until it reaches an artery too small for it to pass through. Signs and symptoms depend on the area of the brain that is blocked.
A hemorrhagic stroke can occur when there is bleeding in the brain. Hemorrhagic strokes are less common than ischemic strokes and symptoms are usually sudden and intense.
There are two types of hemorrhagic stroke:
An intracerebral hemorrhage occurs when a blood vessel within the brain bursts and blood leaks into the brain. The most common cause is high blood pressure.
A subarachnoid hemorrhage occurs when a blood vessel just outside the brain bursts and blood leaks into the area around the brain (called the subarachnoid space). Subarachnoid hemorrhage is caused by a blood vessel abnormality, such as an aneurysm. An aneurysm develops when a point in the wall of an artery (a blood vessel that carries blood away from the heart) weakens. When this happens, blood pushes on the thinned spot, causing it to swell out like a balloon. The more the wall swells, the thinner it becomes. Over time, the wall of the artery may become thinner and may burst, causing a hemorrhagic stroke.
Learn more about aneurysms.