Overview

A subarachnoid hemorrhage is bleeding in the space between the brain and the tissues that cover the brain. The space is known as the subarachnoid space. A subarachnoid hemorrhage is a type of stroke. It is a medical emergency that needs treatment right away.

The primary symptom of a subarachnoid hemorrhage is a sudden, very bad headache. Some people describe it as the worst headache they have ever felt. A subarachnoid hemorrhage also may cause nausea, vomiting, a stiff neck and other symptoms.

Bleeding usually happens when an irregular bulge in a blood vessel, known as an aneurysm, bursts in the brain. Bleeding also can happen because of a head injury. Sometimes a tangle of blood vessels in the brain, known as an arteriovenous malformation, causes the bleeding. And other health conditions, including conditions that affect the blood vessels, can cause bleeding.

If a subarachnoid hemorrhage isn't treated, it can lead to permanent brain damage or death, so it's important to get treatment right away.

Symptoms

The most common symptom of a subarachnoid hemorrhage is a very sudden, very bad headache. The headache starts in a split second and becomes very painful right away. Some people describe it as the worst headache they have ever had.

Along with a sudden headache, symptoms may include:

  • Nausea.
  • Vomiting.
  • Stiff neck or neck pain.
  • Changes in vision.
  • Brief loss of consciousness.

When to see a doctor

A subarachnoid hemorrhage is a medical emergency.

Get immediate medical attention if you experience a very sudden, very bad headache or if you have other symptoms of a subarachnoid hemorrhage. This is especially important if you have been diagnosed with a brain aneurysm or if you have experienced a head injury.

If you're with someone who complains of a very bad headache that came on suddenly or who loses consciousness, call 911 or your local emergency number.

Causes

A subarachnoid hemorrhage may be caused by:

  • A brain aneurysm that bursts. A brain aneurysm is a bulge in a blood vessel in the brain. The aneurysm can burst and cause bleeding in the space between the brain and the tissues covering the brain, known as the subarachnoid space. A brain aneurysm is the most common cause of a subarachnoid hemorrhage.
  • Head injury. Another common cause is a head injury. A head injury from an auto accident, fall or violence can lead to a subarachnoid hemorrhage.
  • A tangle of blood vessels in the brain, known as an arteriovenous malformation. This irregular tangle of blood vessels can rupture and cause bleeding in the brain.
  • Swelling of the blood vessels, known as vasculitis. This can cause the walls of the blood vessels to thicken and narrow. Vasculitis can lead to a blood clot or an aneurysm.

Risk factors

Some risk factors for a subarachnoid hemorrhage are not under your control. They include:

  • Being an older age. Most subarachnoid hemorrhages that result from an aneurysm occur in people between ages 55 and 60. Women in their 50s and 60s, in particular, have a higher risk.
  • Having a first-degree relative with a brain aneurysm. This includes a parent, child or sibling related by blood
  • Having certain health conditions. Conditions that increase the risk of a subarachnoid hemorrhage include Ehlers-Danlos syndrome, Marfan syndrome, neurofibromatosis type 1 and polycystic kidney disease.

People who have two or more first-degree relatives with brain aneurysms or who have had a subarachnoid hemorrhage can get screened.

Other risk factors for a subarachnoid hemorrhage can be avoided. They include:

  • Having high blood pressure.
  • Smoking.
  • Misusing alcohol.
  • Using drugs such as cocaine and methamphetamine.
By Mayo Clinic Staff