Hemorrhage also occurs when arterial walls break open. Plaque-encrusted artery walls eventually lose their elasticity and become brittle and thin, prone to cracking. Hypertension, or high blood pressure, increases the risk that a brittle artery wall will give way and release blood into the surrounding brain tissue. AVMs are a tangle of defective blood vessels and capillaries within the brain that have thin walls and can therefore rupture. Bleeding from ruptured brain arteries can either go into the substance of the brain or into the various spaces surrounding the brain.
Intracerebral hemorrhage occurs when a vessel within the brain leaks blood into the brain itself.
Subarachnoid hemorrhage is bleeding under the meninges, or outer membranes, of the brain into the thin fluid-filled space that surrounds the brain. The subarachnoid space separates the arachnoid membrane from the underlying pia mater membrane. In a subarachnoid hemorrhage, one of the small arteries within the subarachnoid space bursts, flooding the area with blood and contaminating the cerebrospinal fluid. Since the CSF flows throughout the cranium, within the spaces of the brain, subarachnoid hemorrhage can lead to extensive damage throughout the brain. In fact, subarachnoid hemorrhage is the most deadly of all strokes.