What Is a Subarachnoid Hemorrhage?

A subarachnoid hemorrhage is a type of bleeding stroke that happens between your brain and the membrane that surrounds it. (This area is called the “subarachnoid” space; “hemorrhage” means bleeding.) It can happen when an artery is damaged and starts to bleed.

Like any stroke, it’s an emergency. Call 911 right away if you or anyone near you show signs. It may feel like the worst headache you’ve ever had. You may also have symptoms such as:

  • Nausea, vomiting, or both
  • Stiff neck
  • Double vision
  • Trouble talking
  • Drooping eyelid
  • Confusion
  • Sensitivity to light
  • Seizures
  • Loss of consciousness
  • Weakness on one side of the body or other stroke-like symptoms

Don’t delay -- call 911 right awy.


The most common cause is of a subarachnoid hemorrhage is an aneurysm. This is a weak place in a blood vessel, which may bulge or balloon out and eventually break.

Other reasons why a subarachnoid hemorrhage can happen include an arteriovenous malformation (a tangled connection of arteries and veins in your brain) or a head injury, such as from a car accident or fall.


You may get one or more of these imaging tests to see if there’s bleeding in your brain:

CT scan. Computed tomography uses a series of X-rays combined by a computer to form an image that’s more detailed than a single X-ray. You may get a contrast dye by IV to provide better images. A CT scan doesn’t always show a small subarachnoid hemorrhage or one that happened a week or more ago.

MRI. Magnetic resonance imaging uses a large magnet and radio waves to create images of your brain. You might get a contrast dye by IV to enhance the images. It can reveal bleeding that’s happened in the recent past.

Other tests that can help with diagnosis include:

Cerebral angiogram. You’ll get a catheter (a thin, flexible tube) placed into an artery in your leg and threaded up to your brain. Then you’ll get a contrast dye by IV to highlight the blood vessels in your brain on X-rays.

Spinal tap. Also called a lumbar puncture, a health care worker will put a needle into your back to collect some spinal fluid to check for blood.

You may need to repeat imaging tests, such as the CT scan, because bleeding doesn’t always show up right away.



If you have a subarachnoid hemorrhage, you’ll be hospitalized right away, preferably at a center that treats strokes.

At the hospital, you may get medications to ease your headache and to help prevent seizures and clot-related (“ischemic”) strokes that can happen when an artery is blocked. Doctors will try to keep your blood pressure high enough to keep blood flowing in your brain but low enough to stop excessive bleeding. If you have too much fluid in the brain, doctors may need to put in a shunt. This thin, flexible tube drains the extra fluid and prevents pressure on the brain.

If you have an aneurysm that has burst, you may get one of the following procedures to stop or prevent further bleeding:

Endovascular coiling. Using the catheter in a cerebral angiogram, your doctor will put a tiny coiled wire into the aneurysm, where it forms a clot that stops the bleeding.

Endovascular stent. Instead of a coil, you’ll get a tiny tube called a stent placed across the aneurysm. The stent channels the blood away from the aneurysm to prevent it from leaking or bursting.

Clip. You doctor will make a surgical cut (incision) in your scalp and remove a piece of your skull to reach the aneurysm. A special microscope will help your doctor find the aneurysm and fasten a tiny clip across it, replace the piece of skull, and sew up the surgical cut.

Vessel bypass. A surgeon will attach a blood vessel to the artery past the aneurysm to ensure good blood flow in the brain, once the aneurysm has been repaired. The bypass artery may come from inside of your brain or scalp, or from your arm or leg.

Things That Make These Strokes More Likely

It’s not possible to prevent all subarachnoid hemorrhages. But if aneurysms run in your family, tell your doctor. You may need to get tested to find out if you have any cerebral aneurysms that haven’t burst open.

These things raise your risk for a subarachnoid hemorrhage. Addressing these may help you prevent one:


WebMD Medical Reference Reviewed by Melinda Ratini, DO, MS on July 09, 2019



Steve Arkin, MD, neurologist, Miami Valley Hospital, Dayton, OH.

Mayo Clinic: “Subarachnoid hemorrhage,” “Arteriovenous malformation,” “CT scan,” “MRI.”

Harvard Medical School: “Subarachnoid Hemorrhage.”

Brain Aneurysm Foundation: “Statistics and Facts.”

Johns Hopkins Medicine: “Subarachnoid Hemorrhage.”

UCLA Health: “Subarachnoid Hemorrhage.”

Mount Sinai Cerebrovascular Center: “Subarachnoid Hemorrhage.”

The Internet Stroke Center: “How a Stroke is Diagnosed.”

Cleveland Clinic: “Subarachnoid Hemorrhage (SAH): Diagnosis and Tests,” “Subarachnoid Hemorrhage: Management and Treatment.”

Merck Manual (consumer version): “Subarachnoid Hemorrhage.”

National Institute of Neurological Disorders and Stroke: “Cerebral Aneurysms Fact Sheet.”

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