While an ischemic stroke is caused by the blood supply to part of the brain being cut off, a hemorrhagic stroke is caused by bleeding into the brain. A subarachnoid hemorrhage is sudden bleeding between the brain and the membranes that cover it. Besides killing the brain cells where the bleeding occurs, bleeding inside the skull can quickly raise the pressure on the brain to dangerous levels.
Subarachnoid hemorrhage can be caused by any of several factors:
- A head injury. This is the most common cause of an intracranial hemorrhage in people younger than 50.
- Arteriovenous malformation. This is an anatomical abnormality in the arteries or veins in or around the brain. It may be present from birth, but it is only identified if symptoms occur. Bleeding from an arteriovenous malformation can cause sudden collapse and death. It tends to strike teenagers and young adults.
- An aneurysm. This is a weakness in the wall of an artery causing a pouch or a swelling in the blood vessel. The thin walls of an aneurysm can burst and cause a hemorrhage.
- An infection
There usually are few symptoms of an aneurysm that causes a subarachnoid hemorrhage. Sometimes these aneurysms press on a nerve or leak small amounts of blood before a major rupture, thus producing warning signs. These symptoms, which can occur minutes to weeks before a rupture, include:
- Severe headache
- Facial pain
- Double vision, droopy eyelid or other vision problems
If these symptoms are present, they should always be brought to a doctor’s attention quickly so that steps can be taken to prevent a massive hemorrhage.
An actual rupture can produce the following symptoms:
- A sudden, severe headache
- A brief loss of consciousness that often follows the onset of the headache. Some people remain in a coma, but most often patients wake up feeling confused and sleepy. Within a few minutes or few hours, the patient may again begin to feel confused and sleepy.
- Frequent fluctuations in the heart beat and breathing rate often occur
- Paralysis on one side of the body or neurologic problems (this usually occurs in about 25% of the people who have subarachnoid hemorrhages)
Diagnosis and Natural History
The diagnosis of a subarachnoid hemorrhage can usually be made with a computed tomography (CT) scan. If the CT scan is not conclusive, a lumbar puncture (spinal tap) can be done to confirm or rule out the diagnosis.
About a third of those who have a subarachnoid hemorrhage die during the hemorrhage because of extensive brain damage. Without proper treatment for the aneurysm, 20% to 30% will have a second bleed within the first month, and those who survive 3 months have approximately a 3% chance every year of having another episode of bleeding. Recurrent bleeding has a 70% mortality rate. Because of the ominous prognosis with delayed definitive therapy, referral to a center of excellence with experience in treating subarachnoid hemorrhage is imperative.
Symptoms of a subarachnoid hemorrhage require emergency evaluation and treatment. If a subarachnoid hemorrhage is confirmed and the patient is medically and neurologically stable, members of the stroke team will confer about the timing and choice of the best diagnostic and treatment options. Usually, magnetic resonance angiography (MRA), CT angiography (CTA) and/or contrast angiography are used to determine the exact size and location of the aneurysm. Depending on the results, an interventional radiology, neurosurgical or combination approach is chosen. It is critical to have doctors with the experience, judgment and technical know-how to make the right choices for each patient.