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).
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The most common cause is rupture of a bulge (aneurysm) in an artery.
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Usually, rupture of an artery causes a sudden, severe headache, often followed by a brief loss of consciousness.
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Computed tomography or magnetic resonance imaging, sometimes a spinal tap, and angiography are done to confirm the diagnosis.
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Drugs 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
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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.
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Causes
Subarachnoid hemorrhage usually results from head injuries.
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:
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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. 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) 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.
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.
Symptoms
Before rupturing, an aneurysm usually causes no symptoms. However, it can cause symptoms if it does one of the following:
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Presses on a nerve (often one that controls eye movement, causing double vision)
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Leaks small amounts of blood, causing a headache, typically one that differs from past headaches
The following can be early warning signs before a large rupture:
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Double vision
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A headache that is sudden and severe and differs from past headaches
These warning signs for 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:
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Headache, which may be unusually sudden and severe (sometimes called a thunderclap headache)
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Facial or eye pain
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Double vision
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Blurred vision
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A stiff neck
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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 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 other serious problems (complications) such as the following:
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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.
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Vasospasm: Vasospasm is sudden 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.
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A second rupture: Sometimes the aneurysm ruptures a second time, usually within a week and with catastrophic results.
Diagnosis
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Computed tomography or magnetic resonance imaging
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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
(lumbar puncture) is done if CT is inconclusive or unavailable. 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.
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. Magnetic resonance angiography or CT angiography may be used instead. 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.
Prognosis
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. Surgery
to treat the aneurysm 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.
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, loss of sensation on one side of
the body, or difficulty using and understanding language, despite timely
treatment.
Treatment
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Drugs to relieve the headache
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Measures to treat or prevent complications
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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 drugs (such as aspirin) are not given because they make the bleeding worse.
Pain relievers (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. 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 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.
Shunt in Hydrocephalus
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.
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.
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.
One of the following surgical procedures (called endovascular surgery) is used to repair an aneurysm:
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Endovascular coiling
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Endovascular stenting
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Less commonly, use of metal clip
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 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. 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.
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