Subarachnoid Hemorrhage

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.

What is the difference between subarachnoid hemorrhage and subdural hematoma?

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.

Who do subarachnoid hemorrhages affect?

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:

• An unruptured aneurysm in your brain or elsewhere in your body.
• History of a previously ruptured brain aneurysm.
• Cigarette smoking.
• High blood pressure (hypertension).
• Fibromuscular dysplasia (FMD), Ehlers-Danlos syndrome and other connective tissue conditions.
• History of polycystic kidney disease.
• Cocaine and/or methamphetamine use.
• Excessive alcohol consumption.
• Use of blood thinners, such as warfarin.
• A strong family history of aneurysms.

How common is subarachnoid hemorrhage (SAH)?

Approximately 10 to 14 out of 100,000 people per year experience a subarachnoid hemorrhage in the United States.