An ischemic stroke happens when a blood clot blocks an artery to the brain. The brain does not get the oxygen rich blood, and brain cells begin to die within minutes. Over 80 percent of strokes are ischemic. Uncontrolled high blood pressure increases the risk for ischemic stroke. There are two types:
- Thrombotic stroke is the most common type of ischemic stroke. A blood clot (thrombus) forms inside an artery that supplies blood to the brain. Blocked carotid arteries of the neck (or other brain arteries) are most often the cause.
- Embolic stroke occurs when a blood clot or small piece of plaque (embolus) forms in another part of the body and travels to the brain. Atrial fibrillation increases the risk for embolic stroke.
Hemorrhagic Stroke
A hemorrhagic stroke happens when a blood vessel in the brain breaks and bleeds into the brain. This causes brain cells to die. Less than 20 percent of strokes are hemorrhagic. There are two types:
- Intracerebral hemorrhage happens when a blood vessel breaks and bleeds into the brain tissue. Having high blood pressure for many years can change artery walls and cause this type of stroke.
- Subarachnoid hemorrhage refers to bleeding in the space between the surfaces of the brain and the skull. This causes increased pressure in the brain and injures brain cells. One of the most common causes of this type of stroke is a ruptured aneurysm.