A hemorrhagic stroke is bleeding (hemorrhage) that suddenly interferes with the brain's function. This bleeding can occur either within the brain or between the brain and the skull. Hemorrhagic strokes account for about 20% of all strokes, and are divided into categories depending on the site and cause of the bleeding:
Intracerebral hemorrhage — Bleeding occurs from a broken blood vessel within the brain. Some things that increase your risk for this kind of hemorrhage are high blood pressure (hypertension), heavy alcohol use, advanced age and the use of cocaine or amphetamines.
Other kinds of stroke can convert to an intracerebral hemorrhage. For example, a stroke that begins without hemorrhage (a thrombotic or embolic stroke) can lead to intracerebral hemorrhage shortly afterward. This is especially common for embolic strokes that are related to a heart valve infection (endocarditis). In this case, a clump of bacteria and inflammatory cells from the valve infection can become a floating mass within the bloodstream (called an embolus). The infected clump can travel into a brain artery and become wedged there. Then, the infection can spread through the artery.
In rare cases, intracerebral hemorrhage may happen because of a leaking arteriovenous malformation (AVM), which is an abnormal and weak-walled blood vessel that connects an artery and a vein. This weak blood vessel is present from birth—it is larger than a capillary so blood that flows in can be at high pressure, causing the AVM to eventually stretch or leak.
Subarachnoid hemorrhage — Bleeding from a damaged blood vessel causes blood to accumulate at the surface of the brain. Blood fills a portion of the space between the brain and the skull, and it mixes with the cerebrospinal fluid that cushions the brain and spinal cord. As blood flows into the cerebral spinal fluid, it increases pressure on the brain, which causes an immediate headache. In the days immediately following the bleeding, chemical irritation from clotted blood around the brain can cause brain arteries that are near to this area to go into spasm. Artery spasms can damage brain tissue. Most often, a subarachnoid hemorrhage happens because of a leaking saccular aneurysm (a sack-like bulge in the wall of an artery), but it also can occur because of leakage from an arteriovenous malformation.