Subarachnoid hemorrhage: Symptoms, causes, and diagnosis

A subarachnoid hemorrhage occurs when blood leaks into the space between two of the membranes surrounding the brain. A swollen blood vessel, or aneurysm, usually ruptures and causes the condition.

A hemorrhage of this type can lead to a stroke and often has severe consequences. Bleeding can happen suddenly, causing an extreme headache. Frequently, the cause is a ruptured cerebral aneurysm or a head injury.

Subarachnoid hemorrhage occurs in approximately 10 in every 100,000 people in the United States, equivalent to around 30,000 new cases each year.

What is it?

subarachnoid hemorrhage
A subarachnoid hemorrhage can lead to a stroke.

Three membranes surround the brain. The pia mater is the innermost one while the dura mater is the outermost layer.

In between these two is the arachnoid membrane.

The bleeding in subarachnoid hemorrhage occurs in the arteries just below the arachnoid membrane and above the pia mater.

Cerebrospinal fluid fills the part of the brain known as the subarachnoid space. During a subarachnoid hemorrhage, the cerebrospinal fluid in the subarachnoid space fills with blood.

Subarachnoid hemorrhages are responsible for around 5 percent of all strokes and around one in every four deaths caused by or related to strokes.


The first symptom of a subarachnoid hemorrhage is often a sudden and severe “thunderclap headache.”

People describe the pain as similar to receiving a blow on the head and the worst headache of their life. The headache typically throbs near the back of the head.

Other symptoms include:

stiff neck



slurred speech

depression, confusion, delirium, or apathy

impaired consciousness, sometimes loss of consciousness


intraocular hemorrhage, or bleeding into the eyeball

occasional difficulty lifting an eyelid

sharp rise in blood pressure

The headache and stiff neck are similar to meningitis symptoms. However, a subarachnoid hemorrhage does not cause a skin rash or fever.

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