Ischemic Stroke
Ischemic stroke accounts for about 87% of all stroke cases. Ischemic strokes occur as a result of an obstruction in the blood vessels supplying blood to the brain. This is usually caused from the development of fatty deposits lining the vessel walls, or atherosclerosis. These fatty deposits can cause two types of obstruction:
Cerebral thrombosis: a thrombus (blood clot) that develops at the clogged part of the blood vessel.
Cerebral embolism: a blood clot that forms at another location in the circulatory system, usually the heart and large arteries of the upper chest and neck. A portion of the blood clot breaks loose, enters the bloodstream and travels through the brain's blood vessels until it reaches vessels too small to let it pass. A second important cause of embolism is an irregular heartbeat, known as atrial fibrillation. It creates conditions where clots can form in the heart, dislodge and travel to the brain.
Hemorrhagic Stroke
Hemorrhagic stroke accounts for about 13% of stroke cases. It results from a weakened vessel that ruptures and bleeds into the surrounding brain. The blood accumulates and compresses the surrounding brain tissue. The two types of hemorrhagic strokes are intracerebral hemorrhage and subarachnoid hemorrhage.
Hemorrhagic stroke occurs when a weakened blood vessel ruptures. There are two types of weakened blood vessels that usually cause hemorrhagic stroke: aneurysms and arteriovenous malformations (AVMs).
An aneurysm is a ballooning of a weakened region of a blood vessel. If left untreated, the aneurysm continues to weaken until it ruptures and bleeds into the brain. An arteriovenous malformation (AVM) is a cluster of abnormally formed blood vessels. Any one of these vessels can rupture, also causing bleeding into the brain.
Source: Information on this fact sheet has been prepared and made available to the World Stroke Organization (WSO) by the American Stroke Association, a WSO member organization.