The most common symptom of a subarachnoid hemorrhage is a very sudden, very bad headache. The headache starts in a split second and becomes very painful right away. Some people describe it as the worst headache they have ever had.

Along with a sudden headache, symptoms may include:

• Nausea.
• Vomiting.
• Stiff neck or neck pain.
• Changes in vision.
• Brief loss of consciousness.

When to see a doctor

A subarachnoid hemorrhage is a medical emergency.

Get immediate medical attention if you experience a very sudden, very bad headache or if you have other symptoms of a subarachnoid hemorrhage. This is especially important if you have been diagnosed with a brain aneurysm or if you have experienced a head injury.

If you're with someone who complains of a very bad headache that came on suddenly or who loses consciousness, call 911 or your local emergency number.

A subarachnoid hemorrhage may be caused by:

• A brain aneurysm that bursts. A brain aneurysm is a bulge in a blood vessel in the brain. The aneurysm can burst and cause bleeding in the space between the brain and the tissues covering the brain, known as the subarachnoid space. A brain aneurysm is the most common cause of a subarachnoid hemorrhage.
• Head injury. Another common cause is a head injury. A head injury from an auto accident, fall or violence can lead to a subarachnoid hemorrhage.
• A tangle of blood vessels in the brain, known as an arteriovenous malformation. This irregular tangle of blood vessels can rupture and cause bleeding in the brain.
• Swelling of the blood vessels, known as vasculitis. This can cause the walls of the blood vessels to thicken and narrow. Vasculitis can lead to a blood clot or an aneurysm.

Some risk factors for a subarachnoid hemorrhage are not under your control. They include:

• Being an older age. Most subarachnoid hemorrhages that result from an aneurysm occur in people between ages 55 and 60. Women in their 50s and 60s, in particular, have a higher risk.
• Having a first-degree relative with a brain aneurysm. This includes a parent, child or sibling related by blood
• Having certain health conditions. Conditions that increase the risk of a subarachnoid hemorrhage include Ehlers-Danlos syndrome, Marfan syndrome, neurofibromatosis type 1 and polycystic kidney disease.

People who have two or more first-degree relatives with brain aneurysms or who have had a subarachnoid hemorrhage can get screened.

Other risk factors for a subarachnoid hemorrhage can be avoided. They include:

• Having high blood pressure.
• Smoking.
• Misusing alcohol.
• Using drugs such as cocaine and methamphetamine.

To diagnose a subarachnoid hemorrhage, you may need the following tests:

• CT scan. This imaging test is very effective at detecting bleeding in the brain. But it may not detect bleeding if you have a low red blood cell count or if there is a small amount of bleeding. Your healthcare professional may inject a contrast dye to view your blood vessels in greater detail, known as a CT angiogram.
• MRI. This imaging test also can detect bleeding in the brain. An MRI scan may show signs of a subarachnoid hemorrhage in rare cases when it's not detected by a CT scan. Your healthcare professional might inject a dye into a blood vessel to view the arteries and veins in greater detail, known as an MR angiogram.
• Cerebral angiography. You may have a cerebral angiography to get more-detailed images. Angiography also may be done if a subarachnoid hemorrhage is suspected, but the cause isn't clear or doesn't appear on other imaging. A long, thin tube known as a catheter is inserted into an artery and threaded to your brain. Dye is injected into the blood vessels of your brain to make them visible under X-ray imaging. Sometimes a cerebral angiogram does not show an aneurysm. If this happens, you may have a second angiogram if your healthcare professional thinks an aneurysm is likely.

For some people with an aneurysm that caused a subarachnoid hemorrhage, the bleeding may not appear on initial imaging. If this happens, you may need a lumbar puncture. During this procedure, a needle is inserted into the lower back. A small amount of the fluid that surrounds the brain and spinal cord, known as cerebrospinal fluid, is removed. The fluid is then studied to look for blood, which may mean that you have a subarachnoid hemorrhage.

Treatment of a subarachnoid hemorrhage focuses on stabilizing the condition. Your healthcare team checks your breathing, blood pressure and blood flow.

If you have a burst aneurysm, you're treated for it and your healthcare team works to prevent complications.

To treat a ruptured brain aneurysm, your healthcare professional might recommend:

• Surgery. The surgeon makes an incision in the scalp and locates the brain aneurysm. A metal clip is placed on the aneurysm to stop the blood flow to it.
• Endovascular embolization. The surgeon inserts a catheter into an artery and threads it to your brain. Detachable platinum coils are guided through the catheter and placed in the aneurysm. The coils reduce blood flow into the aneurysm and cause the blood to clot. Different types of coils have been developed to treat aneurysms.
• Other endovascular treatments. Certain aneurysms can be treated with endovascular embolization that uses newer technology. These newer techniques include stent-assisted or balloon-assisted coiling or devices that divert blood flow.

Treating the ruptured aneurysm quickly can help prevent bleeding from happening again.

It's also important to prevent other complications. A subarachnoid hemorrhage may lead to low salts such as sodium in the blood. It also may cause high or low blood sugar. Your healthcare team monitors these levels and treats them if needed.

There also may be poor blood flow to the brain. A common complication of a subarachnoid hemorrhage due to a burst aneurysm is a constriction and narrowing of the blood vessels in the brain, known as vasospasm. This can cause a stroke if blood flow decreases to a certain level. A stroke may be avoided by raising blood pressure or by widening blood vessels in the brain with medicines. The medicine nimodipine (Nymalize) also can lower the risk of vasospasm.

Another common complication is a buildup of fluid in cavities within the brain, known as hydrocephalus. This can be treated with drains inserted in the head or lower back.

Sometimes, procedures need to be repeated. After your initial treatment, follow-up appointments with your healthcare team are important to watch for any changes. You also may need physical, occupational and speech therapies.

A subarachnoid hemorrhage is a medical emergency, so it is likely to be treated in the emergency department. Doctors who specialize in the brain and nervous system may be involved in your care. These specialists may include neurologists, neurosurgeons and neuroradiologists.

What you can do

To make the most of your time with your healthcare team, be ready with the following information. Make a list of:

• Your symptoms, including any that seem unrelated to the reason for seeking medical care.
• Key personal information, including major stresses, recent life changes and family medical history.
• All medicines, vitamins or other supplements you take, including the doses.
• Questions to ask your healthcare team.

For subarachnoid hemorrhage, some basic questions to ask your healthcare professional include:

• What's likely causing my symptoms?
• Other than the most likely cause, what are other possible causes for my symptoms?
• What tests do I need?
• Is my condition likely short-term or long-lasting?
• What's the best course of action?
• What are the alternatives to the primary approach you're suggesting?
• I have these other health conditions. How can I best manage them together?
• Are there restrictions I need to follow?
• Should I see a specialist?
• Are there brochures or other printed material I can have? What websites do you recommend?

Don't hesitate to ask other questions.

What to expect from your doctor

Your healthcare professional is likely to ask you several questions, such as:

• When did your symptoms begin?
• Have your symptoms been constant, or do they come and go?
• How serious are your symptoms?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?