Subarachnoid hemorrhage occurs in approximately 1 out of 10,000 people. About 5 to 10% of strokes are caused by subarachnoid hemorrhage. It is most common in people 20 to 60 years old. It is slightly more common in women than men.

The most common cause of any form of subarachnoid hemorrhage is trauma. In the case of spontaneous subarachnoid hemorrhage, 95% of the cases are a result of a ruptured aneurysm.

A small percentage of subarachnoid hemorrhages have a nonaneurysmal pattern to them. They occur spontaneously, and are usually localized to the area in the brain called the perimesencephalic cisterns. The usual outcome for this type of hemorrhage is excellent. Unlike the majority of hemorrhages that are caused by arterial ruptures, this type is thought to be caused by a ruptured vein or capillary.

Subarachnoid hemorrhage occurs when there is bleeding into the space between the brain and the arachnoid membrane (the middle membrane covering the brain). This may occur from a ruptured cerebral aneurysm or arteriovenous malformation, but some result from unidentified causes.

Risks include: disorders associated with aneurysm or weakened blood vessels, including a history of polycystic kidney disease, fibromuscular dysplasia (FMD), other connective tissue disorders, aneurysms in other blood vessels, high blood pressure, and smoking.

The disorder may cause permanent brain damage from ischemia (loss of blood flow) or from the presence of blood in and around the tissues of the brain.

• Headache
  • Sudden onset
  • Described as the "worst ever experience"
  • Can be preceded by a popping or snapping sensation in the head
  • Pain described as a new type
  • Generalized pain, often worse near the back of the head
• Nausea and vomiting may accompany the headache
• Decreased consciousness and alertness
  • Temporary or progressively worsens to coma and death
• Difficulty seeing or changes in vision
  • Double vision
  • Blind spots
  • Temporary loss of vision in one eye
• Stiff neck
• Photophobia (light bothering or hurting the eyes)
• Muscle aches (especially neck pain and shoulder pain)
• Seizure or spell
• Difficulty or loss of movement or sensation of a part of the body
• Changes in mood and personality
  • Confusion
  • Irritability

Additional symptoms that may be associated with this disease:

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

A neuromuscular examination usually shows irritated meninges (the tissues covering the brain). The neck may be stiff and movement of the neck may be resisted in all but deeply comatose people. There may be indications of focal neurologic deficit (localized decreases in nerve/brain function).

An examination of the eyes may indicate bleeding in the brain. It may also show decreased eye movements and changes that indicate damage to the 3rd or 6th cranial nerves.

• Head CT scan (preferred) or an MRI that shows blood in the subarachnoid area. This should be performed before lumbar puncture (spinal tap). If the CT shows blood in the subarachnoid space, a lumbar puncture is no longer necessary.
• A cerebrospinal fluid examination (spinal tap) that shows blood.
• Angiography of blood vessels of the brain (cerebral angiography) that shows small aneurysms or other vascular anomaly and the exact location of the bleed.

This disease may also alter the results of CPK isoenzymes.

Treatment goals include lifesaving measures, relief of symptoms, repair of the cause of the bleeding, and prevention of complications.

Treatment for coma or decreased mental status may be required, including positioning, airway protection, and life support, and placement of a drain (small plastic tube into the fluid-filled spaces within the brain—ventricles—to relieve intracranial pressure).

If a person is conscious, strict bedrest may be advised, accompanied by measures to avoid increases in intracranial pressure (pressure in the head). This may include avoiding activities such as bending over, straining, sudden position changes, or similar activities.

Stool softeners or laxatives may prevent straining during bowel movements.

Pain killers and anti-anxiety medications may be used to relieve headache and reduce intracranial pressure. Antihypertensive medications may be used to moderately reduce blood pressure if it is very high. Phenytoin or other medications may be used to prevent or treat seizures. Nimodipine (a calcium channel blocker) is used to prevent vasospasm (spasm of a blood vessel).

Treatment is usually required, which may be either via a craniotomy (opening a hole in the skull) and clipping of the aneurysm (placing a metal clip across the base of the aneurysm so as to separate it from the circulation), or endovascular coiling (placing platinum coils within the aneurysm from the inside of the blood vessel itself). Surgical removal of large collections of blood may also be needed.

Subarachnoid hemorrhage has a variable prognosis (probable outcome) depending on the location and extent of the bleeding and complications. Complete recovery can occur after treatment, but death may occur in some cases with or without treatment.

• Stroke
• Seizures
• Side effects of medications (see the specific medication)
• Complications of surgery

Go to the emergency room or call the local emergency number (such as 911) if symptoms of subarachnoid hemorrhage are present. Emergency symptoms include seizures or breathing difficulties; loss of consciousness; difficulties with speech, vision, movement, or sensation; and eating or swallowing difficulties.

Identification and successful treatment of an incidentally found aneurysm would prevent subarachnoid hemorrhage.