A subarachnoid hemorrhage occurs when bleeding from a damaged blood vessel causes an accumulation of blood at the surface of the brain. This blood enters the space between the brain and the skull, and mixes with the cerebrospinal fluid that cushions the brain and spinal cord. This increases the pressure that surrounds the brain, interfering with brain function.
Subarachnoid hemorrhages affect five to 10 out of every 100,000 people in the United States, most commonly between ages 35 and 60. About 85% of these patients have saccular aneurysms.
Several large arteries form a circle at the base of the brain. When a subarachnoid hemorrhage is caused by a ruptured saccular aneurysm, the aneurysm usually is located where a blood vessel branches from one of these large arteries. About 20% of patients who have had a subarachnoid hemorrhage have multiple aneurysms. Although it is not possible to predict whether an aneurysm will rupture, an aneurysm is more likely to rupture when it has a diameter of 7mm or more. About 11 million people in the United States have at least one saccular aneurysm in the brain, about 25,000 to 30,000 people have a subarachnoid hemorrhage annually.
An Arteriovenous Malformation (AVM) is a tangled, abnormal mesh of blood vessels that connects an artery and a vein in the brain. AVMs form accidentally prior to birth. An AVM can form almost anywhere in the brain or spinal cord, but they are usually near the back of the brain. AVMs can appear in several generations of the same family and are more common in men. Bleeding from an AVM most often occurs between the ages of 10 and 30. If an AVM is too deep to cause bleeding onto the outer surface of the brain (a subarachnoid hemorrhage), it can cause bleeding inside the brain itself (intracerebral hemorrhage).
Most often, a subarachnoid hemorrhage happens because a bulge in the wall of an artery (a saccular aneurysm) ruptures. A subarachnoid hemorrhage also can occur because blood leaks from an abnormal tangle of blood vessels called an AVM.
In most cases, the hemorrhage develops suddenly without any specific trigger or warning. However, subarachnoid hemorrhage occasionally follows intense physical exercise.
Symptoms can include:
If you have a subarachnoid hemorrhage, you probably will be ill enough that you will be evaluated in an emergency room. The doctor will do a physical examination, including a neurological examination, and will check to see if your neck movement is limited or uncomfortable, which can be a sign that there is an irritant such as blood in the spinal fluid.
One of two brain imaging tests will be used: either a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan. A lumbar puncture can confirm that you have a subarachnoid hemorrhage even when the hemorrhage is too small to appear on a CT scan. This test also can test whether you have meningitis, an infection that can cause similar symptoms: a small sample of cerebrospinal fluid is removed from your back and is examined to see if it contains blood.
Another test, called an MRI angiography, can evaluate blood flow to your brain and can be used to detect remaining aneurysms or AVM abnormalities.
You also may have an electrocardiogram (EKG). The dramatic stress on the brain during a subarachnoid hemorrhage can cause some reflex changes in your heart's circulation, so an EKG test may be abnormal.
When a large hemorrhage occurs in or around the brain, the entire brain is in danger because of increasing pressure within the skull. Much of the emergency treatment for hemorrhagic stroke involves measuring and lowering this pressure. A mechanical ventilator frequently is used to cause someone who has had a subarachnoid hemorrhage to breathe faster. This can result in a lower, safer amount of pressure around the brain. A change in the blood's carbon dioxide level after the heavy breathing causes a decrease in the amount of blood flowing into the brain, so there is less pressure overall. The sugar mannitol is used as a medicine injected into a vein to treat a brain hemorrhage because it pulls brain fluid into the bloodstream, which lowers pressure around the brain. If necessary, blood that has collected can be drained through a hole made in the skull bone.
If the pressure in and around the brain is very high, a person's blood pressure must be allowed to stay higher than normal so that blood can be pumped through this elevated pressure zone. Medicines that lower blood pressure may be stopped or reduced.
Many doctors routinely prescribe medication to protect against seizures, and this medicine may be continued for six months or more. Subarachnoid hemorrhages commonly cause arteries nearest to the site of bleeding to spasm and become narrower, so medicines may be used to prevent this reaction. A subarachnoid hemorrhage also causes shifts in the level of electrolytes, especially sodium, in the blood. You may be given medicines or intravenous (in a vein) fluid to keep sodium at a normal level.
If bleeding occurred because of an abnormally formed blood vessel, then surgery may be needed to prevent a hemorrhage in the future. If a surgeon is able to place a surgical clip on the blood, this can repair an aneurysm. An AVM sometimes can be obliterated by a carefully directed beam of radiation, can be removed through surgery, or blood flow through the area can be blocked with the injection of a gluelike substance. Often, a combination of treatments is used.
Early help by an occupational therapist and physical therapist is helpful. These therapists are professionals who can assist a patient to work around a new disability and to regain strength after brain injury. Commonly, hospitalization is followed by a period of residence at a rehabilitation center, where additional intensive therapy may be provided. The goal of rehabilitation is to maximize recovery.
Prevention. It is almost impossible to prevent subarachnoid hemorrhage caused by an aneurysm or AVM, because these blood-vessel abnormalities usually do not cause any symptoms before the hemorrhage occurs. Smoking has been shown to increase the risk of forming an aneurysm, so avoiding smoking may prevent some cases of hemorrhagic stroke.
Some people have proposed screening tests, such as MRI angiography, that would identify aneurysms before they cause a problem. However, this idea has been impractical for most people, because surgery to remove an aneurysm that is not causing any symptoms involves significant risks, and most aneurysms never cause serious bleeding. This screening may make sense for some people who have two or more close relatives who have had bleeding in or around the brain from an aneurysm. Because aneurysm screening is controversial, you should consider the risks of surgery carefully with your doctor before you request a screening test.
Many patients with a subarachnoid hemorrhage do not survive long enough to reach a hospital. Of those who do, about 50% die within the first month of treatment. However, in patients with subarachnoid hemorrhages resulting from AVMs, the risk of death is only about 15%.
One out of five survivors of subarachnoid hemorrhage has another bleeding episode within 14 days if their aneurysm or AVM is not treated quickly. If the aneurysm or AVM is not treated, 50% rebleed within six months. When surgery is used to clip bleeding aneurysms, there is a good chance of success, but there is also a 5% risk of death or long-term disability.
For those who survive a subarachnoid hemorrhage, recovery is slow. Most people do not recover complete functioning within months of a subarachnoid hemorrhage, and up to 50% of people who survive subarachnoid hemorrhage will have persisting neurological disabilities.
Subarachnoid hemorrhages account for about 7% of all strokes.
Call for emergency help immediately whenever a friend or family member shows any unexpected neurological symptoms, especially if that person losses consciousness or suddenly develops a seizure. Also, call your doctor promptly if you develop a severe headache and you are vomiting. Less intense headaches also should be evaluated by your doctor if you have them often or if they are accompanied by symptoms such as nausea, vomiting, weakness or numbness in any part of the body.
If you have a sudden, very severe headache but it goes away, it is still important to discuss this with your doctor. Sometimes blood leaks briefly from a blood vessel six to 20 days before a subarachnoid hemorrhage occurs. The headache this leak causes is called a sentinel headache. Your doctor may be able to provide treatment that can prevent more serious bleeding.
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