There are 2 types of stroke:
- Ischemic stroke is caused by a lack of oxygen in the brain, usually due to a blood clot blocking a blood vessel.
- Hemorrhagic stroke is caused by a ruptured blood vessel in the brain.
Each of these types of stroke has different underlying causes.
Ischemic stroke
Normally, the inside of a blood vessel is smooth, allowing blood to flow easily. Atherosclerosis, or hardening of the arteries, can roughen the wall of the blood vessel. A blood clot may then form on the irregular surface blocking the vessel. Or the clot may dislodge and travel towards the brain blocking the vessel higher up. Risk factors for atherosclerosis include high blood pressure, high cholesterol levels and smoking. In certain types of heart disease with heart rhythm irregularities, blood clots may form in the heart and travel to the brain. The medical term for this is cardiac embolism. A much less common cause of stroke occurs when a person's blood tends to clot more easily than average. In other cases, the cause is unknown.
Hemorrhagic stroke
The most common cause of this type of stroke is high blood pressure. Years of high blood pressure weaken the blood vessel wall eventually causing it to rupture.
In other cases, the blood vessel wall in the brain is abnormal. For example, aneurysms may balloon out from a blood vessel wall. Aneurysms can burst causing a brain hemorrhage. There are several other blood vessel wall abnormalities that cause some people to be more likely to have a brain hemorrhage. Sometimes, the thinness of a person's blood can make them susceptible to hemorrhagic stroke.