A subarachnoid hemorrhage is bleeding in the space between your brain and the surrounding membrane (subarachnoid space). The primary symptom is a sudden, severe headache. The headache is sometimes associated with nausea, vomiting and a brief loss of consciousness.

Bleeding usually results from the rupture of an abnormal bulge in a blood vessel (aneurysm) in your brain. Sometimes bleeding is caused by trauma, an abnormal tangle of blood vessels in your brain (arteriovenous malformation), or other blood vessel or health problems.

Untreated, a subarachnoid hemorrhage can lead to permanent brain damage or death.

To diagnose a subarachnoid hemorrhage, your doctor is likely to recommend:

• CT scan. This imaging test can detect bleeding in your brain.Your doctor may inject a contrast dye to view your blood vessels in greater detail (CT angiogram).
• MRI. This imaging test also can detect bleeding in your brain. Your doctor might inject a dye into a blood vessel to view the arteries and veins in greater detail (MR angiogram) and to highlight blood flow.
• Cerebral angiography. You doctor inserts a long, thin tube (catheter) into an artery in your leg and threads it to your brain. Dye is injected into the blood vessels of your brain to make them visible under X-ray imaging. Your doctor might recommend cerebral angiography to obtain more-detailed images or if a subarachnoid hemorrhage is suspected but the cause isn't clear or doesn't appear on other imaging.

Up to 22% of aneurysmal subarachnoid hemorrhages don't appear on initial imaging tests. If your initial tests don't show bleeding, your doctor might recommend:

• Lumbar puncture. Your doctor inserts a needle into your lower back to withdraw a small amount of fluid that surrounds your brain and spinal cord (cerebrospinal fluid). The fluid is examined for the presence of blood, which can indicate a subarachnoid hemorrhage.
• Repeated imaging. The tests might be repeated several days after the initial testing.

Treatment initially focuses on stabilizing your condition.

If your bleeding is caused by a ruptured brain aneurysm, your doctor might recommend:

• Surgery. The surgeon makes an incision in your scalp and locates the brain aneurysm. A metal clip is placed across the aneurysm's neck to stop the blood flow to it.
• Endovascular embolization. The surgeon inserts a catheter into an artery in your groin and threads it to your brain. Detachable platinum coils are guided through the catheter and placed in the aneurysm. The coils fill the aneurysm, reducing blood flow into the aneurysm sac and causing the blood to clot.
• Other endovascular treatments. Certain aneurysms can be treated with endovascular embolization that uses newer technology such as stent-assisted or balloon-assisted coiling or devices that divert blood flow.

Endovascular procedures sometimes need to be performed again. You'll have regular follow-up appointments with your doctor to watch for any changes. You may also need physical, occupational and speech therapy.