What Is It?
A subarachnoid hemorrhage is bleeding from a damaged artery at the surface of the brain. This bleeding often causes a sudden, severe headache. It is a medical emergency. Subarachnoid hemorrhage is a type of stroke. It can cause permanent brain damage.
Blood from a subarachnoid hemorrhage pulses into the space between the brain and the skull. It mixes with the cerebrospinal fluid that cushions the brain and spinal cord. As blood flows into the cerebral spinal fluid, it increases the pressure that surrounds the brain. The increased pressure can interfere with brain function.
In the days that immediately follow the bleeding, chemical irritation from clotted blood around the brain can cause brain arteries to go into spasm. An artery spasm can cause additional new brain damage.