A subarachnoid hemorrhage is bleeding into the space (subarachnoid space) between the inner layer (pia mater) and middle layer (arachnoid mater) of the tissue covering the brain (meninges).
A subarachnoid hemorrhage is a life-threatening disorder that can rapidly result in serious, permanent disabilities. It is the only type of stroke more common among women than among men.
Subarachnoid hemorrhage usually results from head injuries. However, hemorrhage due to a head injury causes different symptoms, is diagnosed and treated differently, and is not considered a stroke.
Subarachnoid hemorrhage is considered a stroke only when it occurs spontaneously—that is, when the hemorrhage does not result from external forces, such as an accident or a fall. A spontaneous hemorrhage usually results from the sudden rupture of an aneurysm in an artery in the brain. Aneurysms are bulges in a weakened area of an artery's wall. Aneurysms typically occur where an artery branches. Aneurysms may be present at birth (congenital), or they may develop later, after years of high blood pressure weaken the walls of arteries. Most spontaneous subarachnoid hemorrhages result from congenital aneurysms.
Less commonly, subarachnoid hemorrhage results from rupture of an abnormal connection between arteries and veins (arteriovenous malformation) in or around the brain. An arteriovenous malformation may be present at birth, but it is usually identified only if symptoms develop.
Rarely, a blood clot forms on an infected heart valve, travels (becoming an embolus) to an artery that supplies the brain, and causes the artery to become inflamed. The artery may then weaken and rupture.
Before rupturing, an aneurysm usually causes no symptoms unless it presses on a nerve or leaks small amounts of blood, usually before a large rupture (which causes a severe headache). Then it produces warning signs, such as the following:
The warning signs can occur minutes to weeks before the rupture. People should report any unusual headaches to a doctor immediately.
A rupture usually causes a sudden, severe headache that peaks within seconds. It is often followed by a brief loss of consciousness. Almost half of affected people die before reaching a hospital. Some people remain in a coma or unconscious. Others wake up, feeling confused and sleepy. They may also feel restless. Within hours or even minutes, people may again become sleepy and confused. They may become unresponsive and difficult to arouse. Within 24 hours, blood and cerebrospinal fluid around the brain irritate the layers of tissue covering the brain (meninges), causing a stiff neck as well as continuing headaches, often with vomiting, dizziness, and low back pain. Frequent fluctuations in the heart rate and in the breathing rate often occur, sometimes accompanied by seizures.
Severe impairments may develop and become permanent within minutes or hours. Fever, continued headaches, and confusion are common during the first 5 to 10 days.
A subarachnoid hemorrhage can lead to several other serious problems:
If people have a sudden, severe headache that peaks within seconds or that is accompanied by loss of consciousness, confusion, or any symptoms suggesting a stroke, they should go immediately to the hospital.
Computed tomography (CT) is done as soon as possible to check for bleeding. Magnetic resonance imaging (MRI) can also detect bleeding but may not be available immediately.
A spinal tap (lumbar puncture) is done if CT is inconclusive or unavailable. It can detect any blood in the cerebrospinal fluid. A spinal tap is not done if doctors suspect that pressure within the skull is increased enough to make doing a spinal tap risky.
Cerebral angiography (see Table 2: Common Types of Angiography) is done as soon as possible to confirm the diagnosis and to identify the site of the aneurysm or arteriovenous malformation causing the bleeding. Magnetic resonance angiography or CT angiography may be used instead.
About 35% of people who reach the hospital alive die soon after. Some die because the subarachnoid hemorrhage resulted in extensive brain damage. Others die within a few weeks because a second aneurysm ruptures, causing more bleeding. People who survive for 6 months but who do not have surgery for the aneurysm have a 3% chance of another rupture each year. The outlook is better when the cause is an arteriovenous malformation. Occasionally, the hemorrhage is caused by a small defect that is not detected by cerebral angiography because the defect has already sealed itself off. In such cases, the outlook is very good.
Some people recover most or all mental and physical function after a subarachnoid hemorrhage. However, many people continue to have symptoms such as weakness, paralysis, or loss of sensation on one side of the body or aphasia.
People who may have had a subarachnoid hemorrhage are hospitalized immediately. When possible, they are transported to a center that specializes in treating stroke. Bed rest with no exertion is essential. Analgesics such as opioids (but not aspirin or other nonsteroidal anti-inflammatory drugs, which can worsen the bleeding) are given to control the severe headaches. Stool softeners are given to prevent straining during bowel movements. Nimodipine, a calcium channel blocker, is usually given by mouth to prevent vasospasm and subsequent ischemic stroke. Doctors take measures (such as giving drugs and adjusting the amount of intravenous fluid given) to keep blood pressure at levels low enough to avoid further hemorrhage and high enough to maintain blood flow to the damaged parts of the brain. Occasionally, a piece of plastic tubing (shunt) may be placed in the brain to drain cerebrospinal fluid away from the brain. This procedure relieves pressure and prevents hydrocephalus.
For people who have an aneurysm, a surgical procedure is done to isolate, block off, or support the walls of the weak artery and thus reduce the risk of fatal bleeding later. These procedures are difficult, and regardless of which one is used, the risk of death is high, especially for people who are in a stupor or coma. The best time for surgery is controversial and must be decided based on the person's situation. Most neurosurgeons recommend operating within 24 hours of the start of symptoms, before hydrocephalus and vasospasm develop. If surgery cannot be done this quickly, the procedure may be delayed 10 days to reduce the risks of surgery, but then bleeding is more likely to recur because the waiting period is longer.
A commonly used procedure, called endovascular coiling, involves inserting coiled wires into the aneurysm. The coils are placed using a catheter that is inserted into an artery and threaded to the aneurysm. Thus, this procedure does not require that the skull be opened. By slowing blood flow through the aneurysm, the coils promote clot formation, which seals off the aneurysm and prevents it from rupturing. Endovascular coils can be placed at the same time as cerebral angiography, when the aneurysm is diagnosed.
Less commonly, a metal clip is placed across the aneurysm. This procedure prevents blood from entering the aneurysm and eliminates the risk of rupture. The clip remains in place permanently. Most clips that were placed 15 to 20 years ago are affected by the magnetic forces and can be displaced during magnetic resonance imaging (MRI). People who have these clips should inform their doctor if MRI is being considered. Newer clips are not affected by the magnetic forces.
Last full review/revision March 2014 by Elias A. Giraldo, MD, MS