What is a hemorrhage?

A subarachnoid hemorrhage occurs when a blood vessel on the brain's surface ruptures and bleeds into the space between the brain and the skull (but not into the brain itself).

Another type of stroke occurs when a defective artery in the brain bursts, flooding the surrounding tissue with blood. This is a cerebral hemorrhage .

Hemorrhage (or bleeding) from an artery in the brain can be caused by a head injury or a burst aneurysm . Aneurysms are blood-filled pouches that balloon out from weak spots in the artery wall. They're often caused or made worse by high blood pressure. Aneurysms aren't always dangerous, but if one bursts in the brain, a hemorrhagic stroke results.

When a cerebral or subarachnoid hemorrhage occurs, the loss of a constant blood supply means some brain cells no longer can work. Another problem is that accumulated blood from the burst artery may put pressure on surrounding brain tissue and interfere with how the brain functions. Severe or mild symptoms can result, depending on the amount of pressure.

The amount of bleeding determines the severity of cerebral hemorrhages. In many cases, people with cerebral hemorrhages die of increased pressure on their brains. Those who live, however, tend to recover much more than those who've had strokes caused by a clot. The reason is that when a blood vessel is blocked, part of the brain dies - and the brain doesn't regenerate. But when a blood vessel in the brain bursts, pressure from the blood compresses part of the brain. If the person survives, gradually the pressure goes away and the brain may regain some of its former function.