Stroke occurs when a blood vessel bringing blood and oxygen to the brain becomes blocked or ruptures. Deprived of oxygen, brain and nerve cells stop working and begin to die within minutes. The effects of a stroke may be permanent depending on how many cells are lost, where they are in the brain, and how quickly you receive medical treatment.
Ischemic stroke is caused by lack of blood reaching part of the brain. There are three types of ischemic stroke:
- Thrombotic strokes are caused by a blood clot (thrombus) in an artery, blocking blood flow to part of the brain. Blood clots usually form in arteries damaged by plaque.
- Embolic strokes are caused by a wandering clot (embolus) formed elsewhere (usually in the heart or neck arteries). Clots are carried in the bloodstream and block a blood vessel in or leading to the brain.
- Systemic hypoperfusion (low blood flow) happens when the heart’s pumping action fails and too little blood reaches the brain. This is how a heart attack may cause a stroke.
There are two types of hemorrhagic stroke. In both types, a blood vessel ruptures, disrupting blood flow to part of the brain.
- Intracerebral hemorrhages:
- Occur when a blood vessel bleeds or ruptures in deep brain tissue.
- Most often are caused by chronically high blood pressure or aging blood vessels.
- Sometimes are caused by an arteriovenous malformation (AVM), a cluster of abnormally formed blood vessels. Any one of these vessels can rupture, causing bleeding into the brain.
- Subarachnoid hemorrhages:
- Occur when an aneurysm (a blood-filled pouch that balloons out from an artery) on or near the surface of the brain ruptures and bleeds into the space between the brain and the skull.
- Are often caused by high blood pressure.