Subarachnoid hemorrhage (SAH) is bleeding in the space below one of the thin layers that cover and protect your brain. SAH is a medical emergency that requires immediate treatment. It’s often caused by head trauma and/or a ruptured brain aneurysm. The most common sign is a sudden, severe headache.
Subarachnoid hemorrhage (SAH) is bleeding in the area between your brain and the thin tissues that cover and protect it. SAH is a medical emergency.
Your brain has three membrane layers or coverings (called meninges) that lie between your skull and your brain tissue. The outermost layer of your meninges is called the dura mater, the middle layer is the arachnoid and the layer closest to your brain is the pia mater. SAH happens when there’s bleeding below the arachnoid layer.
SAHs are commonly caused by head trauma and/or a ruptured brain aneurysm. They can vary in severity.
The main sign of SAH is a thunderclap headache, which is an extremely painful headache that comes on suddenly, like a clap of thunder. People who have had a thunderclap headache often describe it as the worst headache of their life, unlike any headache they’ve ever experienced.
A subarachnoid hemorrhage is life-threatening. Get immediate medical care if you’re experiencing symptoms of it.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Subarachnoid hemorrhage and subdural hematoma are both types of bleeding in your brain. The difference is where the bleeding occurs.
If you have a subdural hematoma, you’ve experienced a tear in a blood vessel, most commonly a vein, and blood is leaking out of the torn vessel into the space below the dura mater membrane layer. If you have a subarachnoid hemorrhage, blood is leaking into the space below the arachnoid layer. (“Sub-” means “below.”)
Subarachnoid hemorrhage and subdural hematoma have similar symptoms and can both cause brain damage. They’re both medical emergencies.
Subarachnoid hemorrhage (SAH) can happen to anyone, but it most commonly affects people between the ages of 40 and 60.
SAH caused by injury most commonly happens to older people who’ve fallen and hit their heads. Among younger people, the most common injury leading to subarachnoid hemorrhage is vehicle crashes.
Risk factors that make it more likely that you’ll experience subarachnoid hemorrhage include:
Approximately 10 to 14 out of 100,000 people per year experience a subarachnoid hemorrhage in the United States.
The main symptom of a subarachnoid hemorrhage is a thunderclap headache, which is a very intense and painful headache that comes on suddenly.
Call 911 or get to the nearest emergency room if you experience a thunderclap headache, especially if you experience additional symptoms.
Other symptoms of subarachnoid hemorrhage can include:
Subarachnoid hemorrhage is most often caused by head trauma, such as from a serious fall or vehicle accident. Another common cause is a brain aneurysm bursting, resulting in SAH.
A brain aneurysm is a ballooning of an artery in your brain that can rupture and bleed into the space between your brain and skull.
A spontaneous rupture of a brain aneurysm (without head trauma) can also cause SAH. Approximately 85% of non-traumatic SAH cases are due to a ruptured brain aneurysm.
Other, less common causes of SAH include:
If your healthcare provider suspects you have a subarachnoid hemorrhage based on your symptoms and a physical exam, they’ll immediately order a CT (computerized tomography) scan.
A CT scan uses X-rays and a computer to make detailed images of tissues in your body. A CT scan of your brain is an effective way for your provider to see a subarachnoid hemorrhage. Another type of CT scan, CT angiography (CTA), visualizes blood vessels using contrast material injected through a vein.
Sometimes, a CT scan may miss a very small subarachnoid hemorrhage or one that occurred a week or two ago. Your provider will likely order other tests to detect a subarachnoid hemorrhage if a CT scan is negative.
These tests include:
The hospital care following the diagnosis of subarachnoid hemorrhage focuses on both discovering and treating the cause of the SAH, as well as managing its complications.
As brain aneurysms cause over 80% of non-traumatic subarachnoid hemorrhages, your provider will likely order a cerebral angiogram to get images of your brain’s arteries and then treat the aneurysm.
As subarachnoid hemorrhage (SAH) is a life-threatening, emergency condition, it’s typically treated in the intensive care unit (ICU) in a hospital with neurological expertise. The goals of treatment are to:
Life-saving treatment and treatment to manage symptoms may include:
To treat the subarachnoid hemorrhage and its cause, you may need surgery to:
The length of stay in the hospital varies based on your health status. Most people who have a subarachnoid hemorrhage are admitted to the hospital anywhere from 10 to 20 days based on their condition and their need for rehabilitation.
The majority of subarachnoid hemorrhage cases are due to head trauma and/or a ruptured brain aneurysm. Because of this, the best way you can try to avoid experiencing SAH is to manage your risk factors for these two situations.
To try to prevent head trauma, always wear a helmet when riding a bike or motorcycle or when playing high-risk sports. Always drive safely and follow traffic laws. If you’re prone to falls, work with a physical or occupational therapist to learn how to try to prevent them and make your home safer.
To lower your risk of developing a brain aneurysm and/or to prevent an existing aneurysm from rupturing, talk to your healthcare provider about steps you can take to stay healthy. They’ll likely recommend the following:
The prognosis (outlook) for subarachnoid hemorrhage depends on its cause, severity and the presence of other complications or injuries.
It’s a severe condition — half of people who have subarachnoid hemorrhage experience sudden death. Of those who make it to a hospital:
Possible immediate complications of SAH include:
Subarachnoid hemorrhage (SAH) can cause brain damage, which can lead to long-term or even permanent issues. Possible long-term complications of SAH include:
These long-term complications can be managed and treated with several different types of therapies, including:
Certain medications can also help. Talk to your healthcare team if you experience any of these issues.
Life expectancy after a subarachnoid hemorrhage (SAH) varies based on its severity and how quickly it’s diagnosed and treated.
In general, the one-year mortality rate of untreated SAH is up to 65%, meaning up to 65% of people who had an SAH that wasn’t treated died within one year of the episode.
With appropriate diagnosis and treatment, the one-year mortality rate is around 18%.
If you’ve had a subarachnoid hemorrhage (SAH), you’ll likely need to see your healthcare team regularly to monitor your health and progress. You may also need physical, occupational and/or speech therapy after an SAH if you’ve experienced complications due to it.
A note from Cleveland Clinic
A sudden, severe headache could be a sign of a subarachnoid hemorrhage (SAH). This is a serious, life-threatening condition that needs immediate medical attention and emergency treatment. If you have an unruptured brain aneurysm, talk with your healthcare provider about the risks and benefits of different treatment and management options.
Last reviewed by a Cleveland Clinic medical professional on 10/12/2022.
Learn more about our editorial process.