Subarachnoid hemorrhage is bleeding in the area between the brain and the thin tissues that cover the brain. This area is called the subarachnoid space.

Subarachnoid hemorrhage can be caused by:

• Bleeding from an arteriovenous malformation (AVM)
• Bleeding disorder
• Cerebral aneurysm rupture
• Head injury
• Unknown cause (idiopathic)
• Use of blood thinners

Injury-related subarachnoid hemorrhage is often seen in the elderly who have fallen and hit their head. Among the young, the most common injury leading to subarachnoid hemorrhage is motor vehicle crashes.

Subarachnoid hemorrhage due to rupture of a cerebral aneurysm occurs in approximately 10-15 out of 10,000 people. However, some studies suggest that number may be slightly lower. Subarachnoid hemorrhage due to rupture of a cerebral aneurysm is most common in persons age 20 to 60. It is slightly more common in women than men.

Risks include:

• Aneurysms in other blood vessels
• Disorders associated with aneurysm or weakened blood vessels
• Fibromuscular dysplasia (FMD) and other connective tissue disorders
• High blood pressure
• History of polycystic kidney disease
• Smoking

A strong family history of aneurysms may also increase your risk.

The main symptom is a severe headache that starts suddenly and is often worse near the back of the head. Patients often describe it as the "worst headache ever" and unlike any other type of headache pain. The headache may start after a popping or snapping feeling in the head.

Other symptoms:

• Decreased consciousness and alertness
• Difficulty or loss of movement or feeling
• Mood and personality changes, including confusion and irritability
• Muscle aches (especially neck pain and shoulder pain)
• Nausea and vomiting
• Photophobia (light bothers or hurts the eyes)
• Seizure
• Stiff neck
• Vision problems, including double vision, blind spots, or temporary vision loss in one eye

Additional symptoms that may be associated with this disease:

• Eyelid drooping
• Eyes, pupils different size
• Opisthotonos (not very common)
• Seizures

A physical exam may show a stiff neck due to irritated meninges, the tissues that cover the brain. Except those in a deep coma, persons with a subarachnoid hemorrhage may resist neck movement.

A neurological exam may show signs of decreased nerve and brain function (focal neurologic deficit).

An eye exam may show signs of bleeding in the brain. Decreased eye movements can be a sign of damage to the cranial nerves. In milder cases, no problems may be seen on an eye exam.

If your doctor thinks you may have a subarachnoid hemorrhage, a head CT scan (without dye contrast) should be immediately done. In some cases, the scan may be normal, especially if there has only been a small bleed. If the CT scan is normal, a lumbar puncture (spinal tap) must be performed. Patients with SAH will have blood in their spinal fluid.

Cerebral angiography of blood vessels of the brain may show small aneurysms or other vascular problems. This test can pinpoint the exact location of the bleed and can tell if there are blood vessel spasms.

Transcranial doppler ultrasound is used to look at blood flow through the skull. It can also detect blood vessel spasms and may be used to guide treatment.

Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) are occasionally used to diagnose a stroke or tumor.