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Subarachnoid Hemorrhage (SAH)


Andrei V. Alexandrov

, MD, The University of Tennessee Health Science Center;

Balaji Krishnaiah

, MD, The University of Tennessee Health Science Center

Reviewed/Revised Jun 2023
Topic Resources

A subarachnoid hemorrhage is bleeding into the space (subarachnoid space) between the inner layer (pia mater) and middle layer (arachnoid mater) of the tissues covering the brain (meninges).

  • The most common cause is rupture of a bulge (aneurysm) in an artery.

  • Usually, rupture of an artery causes a sudden, severe headache, often followed by a brief loss of consciousness.

  • Computed tomography or magnetic resonance imaging, sometimes a spinal tap, and angiography are done to confirm the diagnosis.

  • Medications are used to relieve the headache and to control blood pressure, and surgery is done to stop the bleeding.

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.

Bursts and Breaks: Causes of Hemorrhagic Stroke

When blood vessels of the brain are weak, abnormal, or under unusual pressure, a hemorrhagic stroke can occur. In hemorrhagic strokes, bleeding may occur within the brain, as an intracerebral hemorrhage. Or bleeding may occur between the inner and middle layer of tissue covering the brain (in the subarachnoid space), as a subarachnoid hemorrhage.

Bursts and Breaks: Causes of Hemorrhagic Stroke

Causes of SAH

Subarachnoid hemorrhage usually results from head injuries Overview of Head Injuries Head injuries that involve the brain are particularly concerning. Common causes of head injuries include falls, motor vehicle crashes, assaults, and mishaps during sports and recreational activities... read more . However, subarachnoid 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 following:

  • The sudden rupture of an aneurysm in an artery in the brain

Aneurysms Brain Aneurysms An aneurysm is a bulge (dilation) in the wall of an artery. Aneurysms that occur in the arteries of the brain (cerebral arteries) are called cerebral aneurysms. Aneurysms may occur in any artery... read more 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. Aneurysms in an artery of the brain can run in families. About 6 to 20% of brain aneurysms may result from an inherited defect in an artery's wall.

Hemorrhage due to a ruptured aneurysm can occur at any age but is most common among people aged 40 to 65.

Less commonly, subarachnoid hemorrhage results from rupture of an abnormal connection between arteries and veins (arteriovenous malformation Brain Arteriovenous Malformations (AVMs) An arteriovenous malformation is a tangle of dilated blood vessels that directly connect arteries and veins, bypassing the capillaries (which normally connect arteries and veins). Brain arteriovenous... read more ) in or around the brain. An arteriovenous malformation may be present at birth, but it is usually identified only if symptoms develop. Subarachnoid hemorrhage can also result from bleeding disorders.

Symptoms of SAH

Before rupturing, an aneurysm usually causes no symptoms. However, it can cause symptoms if it does one of the following:

  • Presses on a nerve (often one that controls eye movement, causing double vision)

  • Leaks small amounts of blood, causing a headache, typically one that differs from past headaches

The symptoms of subarachnoid hemorrhage can occur minutes to weeks before the rupture. People should report any unusual headaches to a doctor immediately.

When a large aneurysm ruptures, it causes the following symptoms:

  • Headache, which may be unusually sudden and severe (sometimes called a thunderclap headache)

  • Facial or eye pain

  • Double vision

  • Blurred vision

  • A stiff neck (usually not immediately)

  • Loss of consciousness

The sudden, severe headache caused by a rupture peaks within seconds. It is often described as the worst headache ever experienced. The headache is often followed by a brief loss of consciousness. Some people die before reaching a hospital. Some people remain unconscious in a coma and ultimately die. 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. People may have seizures Seizure Disorders In seizure disorders, the brain's electrical activity is periodically disturbed, resulting in some degree of temporary brain dysfunction. Many people have unusual sensations just before a seizure... read more .

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 other serious problems (complications) such as the following:

  • Hydrocephalus: Within 24 hours, the blood from a subarachnoid hemorrhage may clot. The clotted blood may prevent the fluid surrounding the brain (cerebrospinal fluid) from draining as it normally does. As a result, blood accumulates within the brain, increasing pressure within the skull. Hydrocephalus may contribute to symptoms such as headaches, sleepiness, confusion, nausea, and vomiting and may increase the risk of coma and death.

  • Vasospasm: Vasospasm is contraction (spasm) of blood vessels. It occurs in about 25% of people, usually about 3 to 10 days after the hemorrhage. Vasospasm limits blood flow to the brain. Then, brain tissues may not get enough oxygen and may die, as in ischemic stroke. Vasospasm may cause symptoms similar to those of ischemic stroke, such as weakness or loss of sensation on one side of the body, difficulty using or understanding language, dizziness, and impaired coordination.

  • A second rupture: Sometimes the aneurysm ruptures a second time, usually within a week and with catastrophic results.

Diagnosis of SAH

  • Computed tomography or magnetic resonance imaging

  • Angiography

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. Testing for a subarachnoid hemorrhage is done as soon as possible. Then, treatment can be started as soon as possible.

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 Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Imaging tests commonly used to diagnose nervous system (neurologic) disorders... read more Spinal Tap (lumbar puncture) is done if CT is inconclusive or if CT is normal but doctors still suspect a subarachnoid hemorrhage. It can detect any blood in the fluid that surrounds the brain and spinal cord (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.

Magnetic resonance angiography Magnetic resonance angiography (MRA) Magnetic resonance imaging (MRI) is a type of medical imaging that uses a strong magnetic field and very high frequency radio waves to produce highly detailed images. During an MRI, a computer... read more Magnetic resonance angiography (MRA) or CT angiography CT angiography Computed tomography (CT) is a type of medical imaging that combines a series of x-rays to create cross-sectional, detailed images of internal structures. In computed tomography (CT), which used... read more CT angiography may be done to diagnose an aneurysm, but cerebral angiography is the most accurate way to detect an aneurysm. Cerebral 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. For cerebral angiography, a thin, flexible tube (catheter) is inserted into an artery, usually in the groin, and threaded through the aorta to an artery in the neck. Then, a substance that can be seen on x-rays (radiopaque contrast agent) is injected to outline the artery. Cerebral angiography is more invasive than magnetic resonance angiography or CT angiography, but it provides more information. However, because CT angiography is less invasive, it has largely replaced cerebral angiography for the diagnosis of aneurysms within the skull.

Cerebral Angiography: Catheter Insertion

Treatment of SAH

  • Medications to relieve the headache

  • Measures to treat or prevent complications

  • A procedure to treat aneurysms

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.

Anticoagulants (such as heparin and warfarin) and antiplatelet medications (such as aspirin) are not given because they make the bleeding worse.

Pain relievers (analgesics) such as opioids are given as needed to control the severe headaches. However, aspirin and other nonsteroidal anti-inflammatory medications are not used because they can worsen the bleeding. Stool softeners are given to prevent straining during bowel movements. Such straining puts pressure on blood vessels within the skull and increases the risk that a weakened artery will rupture.

Nimodipine, a calcium channel blocker, is usually given by mouth to prevent vasospasm and subsequent ischemic stroke. Doctors take measures (such as giving medications 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.

If hydrocephalus develops, a piece of plastic tubing (shunt) may be placed in the brain to drain cerebrospinal fluid away from the brain. This procedure treats hydrocephalus by relieving pressure.

Procedures to treat aneurysms

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 Stupor and Coma Stupor is unresponsiveness from which a person can be aroused only by vigorous, physical stimulation. Coma is unresponsiveness from which a person cannot be aroused and in which the person's... read more .

The best time for surgery is controversial and must be decided based on the person’s situation. If the person can be aroused, 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.

One of the following surgical procedures (called endovascular surgery) is used to repair an aneurysm:

  • Endovascular coiling

  • Endovascular stenting

Endovascular coiling is commonly used. It involves inserting coiled wires into the aneurysm. For this procedure, a catheter is inserted into an artery, usually in the groin, and threaded to the affected artery in the brain. A contrast agent is injected to enable the doctor to make the aneurysm visible on an x-ray. The catheter is then used to place the coils in the aneurysm. Thus, this procedure does not require that the skull be opened. By slowing blood flow through the aneurysm, the coils encourage the formation of blood clots, 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. The coils remain in place permanently.

In endovascular stenting, a catheter is used to place a tube made of wire (stent) across the opening of the aneurysm. The stent reroutes normal blood flow around the aneurysm, preventing blood from entering the aneurysm and eliminates the risk of rupture. The stent remains in place permanently.

Less commonly, a metal clip is placed across the aneurysm. For this procedure, surgeons make an incision in the skin of the head and remove a piece of the skull so that they can see the aneurysm. The clip is then placed across the opening of the aneurysm. This procedure prevents blood from entering the aneurysm and eliminates the risk of rupture. The clip remains in place permanently. Surgical placement of a clip requires spending several nights in the hospital.

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.

Prognosis for SAH

About 35% of people who have a subarachnoid hemorrhage due to a ruptured aneurysm die before they reach the hospital. Another 15% die within a few weeks because the aneurysm starts bleeding again. Procedures to treat the aneurysm (placing a device using a catheter or doing surgery to open the skull) can reduce the risk that the aneurysm will bleed again. Without treatment, people who survive for 6 months have a 3% chance of another rupture each year.

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, loss of sensation on one side of the body, or difficulty using and understanding language, despite timely treatment.

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