The bleeding occurs in the arteries just below the arachnoid membrane and above the pia mater, just below the surface of the skull. It can happen suddenly, often because of a ruptured cerebral aneurysm or a head injury.
It is a serious condition. One in 8 people who have this type of event die before they reach the hospital.
Those most at risk are smokers, cocaine users, heavy drinkers, people with high blood pressure, and those with a close relative who also had a subarachnoid hemorrhage.
It affects between 10 and 15 people per 100,000 in the United States.
What is it?
The first sign of a subarachnoid hemorrhage is often a thunderclap headache.
There are three membranes that surround the brain. The pia mater is the innermost one, the arachnoid is the middle one, and the dura mater is the outermost layer.
An aneurysm is a bulge that develops in a blood vessel, because of a weakness in the blood vessel wall.
The subarachnoid space is filled with cerebrospinal fluid. During a subarachnoid hemorrhage, the cerebrospinal fluid in the subarachnoid space becomes bloody.
According to the National Institutes of Health (NIH), half of all patients who are hospitalized with a subarachnoid hemorrhage will die, 10 percent of them before reaching hospital, others within the following 3 weeks, due to rebleeding. One third of those who survive will be dependent due to severe disabilities.
Middle aged individuals and females are more likely to be affected. Average age at onset is 55 years.
The first symptom of a subarachnoid hemorrhage is often a sudden and severe "thunderclap headache." Patients describe the pain as similar to receiving a blow on the head, and the worst headache of their life. This headache typically pulsates towards the back of the head.
Other symptoms include:
- Stiff neck
- Slurred speech
- Depression, confusion, delirium, and possibly apathy
- Impaired consciousness, sometimes total loss of consciousness
- Intraocular hemorrhage, or bleeding into the eyeball
- Some patients may find it hard to lift an eyelid
- A sharp increase in blood pressure.
Several factors may lead to a subarachnoid hemorrhage.
Up to 80 percent of subarachnoid hemorrhage cases happen when a cerebral aneurysm ruptures.
An aneurysm occurs when part of a blood vessel swells, for example, because of a weakness in the blood vessel wall. As blood pressure grows, the blood vessel balloons out at its weakest point. The larger the swelling becomes, the greater its risk of bursting, or rupturing.
Aneurysms associated with subarachnoid hemorrhages tend to occur in the circle of Willis and its branches, a circle of arteries that supply blood to the brain.
In some people, a congenital defect leads to weak and thin blood vessel walls, increasing the risk of an aneurysm.
People who smoke, drink alcohol regularly in large quantities, or who have high blood pressure that is not properly controlled have a higher chance of experiencing a ruptured aneurysm.
An arteriovenous malformation is a congenital disorder that happens when a complex, tangled web of abnormal arteries and veins develop. They communicate with each other abnormally and are connected by fistulas. It affects the blood vessels in the spinal cord, brainstem, or brain.
It is a significant cause of subarachnoid hemorrhage. Aneurisms can occur on the vessels that lead to arteriovenous malformations.
Arteriovenous malformations may arise due to a problem while the fetus is developing in the womb.
Symptoms do not tend to appear until a hemorrhage occurs.
A severe head injury can cause a subarachnoid hemorrhage. In 2 percent of cases, a close family relative has also had a subarachnoid hemorrhage.
A patient with stiff neck and a severe headache may have a subarachnoid hemorrhage, and will be referred to a neurologist for further diagnostic tests.
An MRI scan will provide a detailed image of the inside of the skull. It may help to identify blood vessel problems and the hemorrhage.
A lumbar puncture involves taking a sample of cerebrospinal fluid from the lower end of the spine with a needle, to see if there is any blood.
Doppler ultrasound is used to monitor the flow of blood in the brain. Unusual changes in blood flow speed could indicate that the arteries in the brain are in spasm, and this can result in further hemorrhaging. In this case, the patient needs immediate treatment.
A CT scan can detect blood around the brain and any problems that may result from that. A colored dye may be injected into the blood to reveal where the bleeding is coming from.
To prevent blood vessels near the ruptured aneurysm from going into spasm, the patient may be given a drug called nimodipine for about 3 weeks. This medication treats hypertension and prevents spasms.
The headache may be treated with morphine.
Neurosurgical clipping is a surgical intervention to seal the aneurysm shut with a small metal clip.
Endovascular coiling involves inserting a catheter or small plastic tube into an artery, usually in the patient's groin or leg. The tube is threaded through blood vessels until it reaches the part of the brain where the aneurysm is located.
Platinum coils are pushed through the tube into the aneurysm. They cut off the flow of blood into the aneurysm, effectively stopping the hemorrhage.
This intervention has a higher success rate, and the patient recovers more quickly, compared with neurological clipping.
The most dangerous complication is cerebral vasospasm, when the blood vessel near the aneurysm goes into spasm, making the hemorrhage worse.
Those who survive a subarachnoid hemorrhage have a high risk of disability afterward.
Left untreated, it can lead to coma and death. Nimodipine can help reduce the risk of this complication significantly.
Patients with vasospasm need good blood flow to the brain.
One approach is to raise blood pressure by pumping fluids into the blood, or by transfusing blood and plasma into the body. This is known as Triple H Therapy: Hypervolemia, hemodilution, and hypertension, but its effectiveness has not been confirmed.
If this does not work, a small balloon may be implanted in an artery and inflated, to open up the vessel and bring the blood supply back.
Around 5 percent of patients who have a stroke experience a seizure within a few weeks, and around 5 percent of patients with subarachnoid hemorrhage will develop epilepsy. The first seizure will normally occur during the first year after the event.
Hydrocephalus is when too much cerebrospinal fluid builds up in the ventricles in the brain. As pressure builds on the brain, this can cause damage.The doctor may have to drain some fluid by placing a tube, or shunt, into the brain.
Long-term outcomes depend on the complications that arise.
Patients with any of the risk factors should discuss ways of reducing their risk with the doctor. Controlling high blood pressure and avoiding drug and alcohol use can help.