Subarachnoid hemorrhage is a type of stroke in which a blood vessel ruptures and blood leaks into the space between the inner two of the three layers of membrane covering the brain (called the meninges).
In most cases, it is due to the rupture of an aneurysm—a swollen, weakened area at the junction between two arteries in the brain.
In some people, bleeding is due to malformed blood vessels. Either problem may be present from birth.
A subarachnoid hemorrhage may also occur spontaneously or after unaccustomed exercise.
The bleeding typically causes a sudden, violent headache, with vomiting, stiff neck, and sensitivity to bright light.
A person with these symptoms should seek urgent medical attention. These symptoms may be followed by confusion, seizures (fits), unconsciousness, and coma. Treatment is with medication and surgery.
However, full recovery does not always occur, and many cases are fatal.