Idiopathic intracranial hypertension is characterized by increased pressure within the skull (intracranial pressure). What triggers the disorder is unknown.
Idiopathic intracranial hypertension occurs in only about 1 of 100,000 people, usually in women during their reproductive years. However, among young overweight women, it is 20 times more common. As more and more people are becoming overweight, the disorder is becoming more common.
What causes pressure within the skull to increase is unknown. However, certain people are more susceptible to it because the large veins (venous sinuses) that help drain blood from their brain are smaller than in most people. In these people, blood drains from the brain more slowly, causing a back-up of blood in the brain and/or within the skull.
Exactly how being overweight contributes to increased pressure within the skull is unknown. But excess fat in the abdomen may increase pressure in the chest, and blood may not flow from the head to the chest as it normally does. Thus, pressure within the skull may increase.
The increased pressure does not result from other identifiable disorders, such as tumors, infections, blood clots, or blockages that prevent the fluid that surrounds the brain (cerebrospinal fluid) from draining as it normally does.
In most people, the development of idiopathic intracranial hypertension cannot be traced to any particular event. In children, this disorder sometimes develops after corticosteroids are stopped or after growth hormone is used. Sometimes the disorder develops after people take tetracycline antibiotics or large amounts of vitamin A.
Idiopathic intracranial hypertension usually begins with a daily or almost daily headache, which affects both sides of the head. At first, the headache may be mild, but it varies in intensity and may become severe. The headache may be accompanied by nausea, double or blurred vision, and noises within the head that occur with each beat of the pulse (called pulsatile tinnitus). A few people do not have any symptoms.
Increased pressure within the skull may cause the optic nerve to swell near the eyeball—a condition called papilledema. Doctors can observe the swelling by looking at the back of the eye through an ophthalmoscope.
The first sign of vision problems is loss of peripheral (side) vision. People may not notice this loss at first. As a result, people may bump into objects for no apparent reason. Late in the disorder, vision becomes blurred, and people may quickly become blind. As many as one third of people lose their vision, partially or completely, in one or both eyes. Once vision is lost, it usually does not return, even if the pressure around the brain is relieved. In some people, the disorder becomes chronic and progressively worse, increasing the risk of blindness. Doctors closely monitor and treat such people to prevent loss of vision.
Idiopathic intracranial hypertension recurs in about 10 to 20% of people.
Doctors suspect idiopathic intracranial hypertension based on symptoms and results of a physical examination. Sometimes doctors suspect it when they detect papilledema during a routine examination with an ophthalmoscope.
If doctors suspect idiopathic intracranial hypertension, they check the field of vision (the entire area of vision that is seen out of each eye), including peripheral vision. They also examine the interior of the eye with an ophthalmoscope if they have not already done so.
An imaging test, usually magnetic resonance imaging (MRI), is done. One type of MRI (called magnetic resonance venography) can provide images of the large veins (called venous sinuses) that carry blood from the brain. Magnetic resonance venography enables doctors to determine whether these veins are narrowed. These veins are often narrowed in people with idiopathic intracranial hypertension.
A spinal tap (lumbar puncture) is done to measure the pressure of cerebrospinal fluid and to analyze the fluid. In idiopathic intracranial hypertension, the pressure of the fluid is increased, often to very high levels. The content of the fluid is usually normal. As soon as spinal fluid is removed during the spinal tap, the pressure inside the head decreases, the venous sinuses may widen, and more blood may flow from the brain. As a result, the headache lessens.
These and other tests can help identify or rule out other possible causes of increased pressure within the skull (such as a brain tumor blocking the venous sinuses).
Idiopathic intracranial hypertension occasionally resolves without treatment.
Treatment of idiopathic intracranial hypertension focuses on the following:
Drugs known to trigger the disorder, such as tetracycline, should be stopped.
Aspirin, acetaminophen, or drugs used to treat migraines may relieve the headache. Topiramate can also help people lose weight and help lower the pressure within the skull.
Overweight people should lose weight because doing so may reduce pressure within the skull. Idiopathic intracranial hypertension may resolve when as little as 10% of body weight is lost. However, weight reduction programs are often unsuccessful.
Doctors often prescribe acetazolamide to help reduce the pressure. This drug can help reduce pressure within the skull in two ways:
The usefulness of doing spinal taps daily or weekly to remove cerebrospinal fluid is debated. If this treatment is used, people are closely monitored to determine whether pressure is decreasing.
Because peripheral vision is lost before people notice it, an ophthalmologist periodically checks vision, including peripheral vision, using an automated device (called perimetry). The device produces a visual stimulus (such as a flash of light) and records the person”s responses. Results are very accurate. This periodic testing enables doctors to identify problems with vision as soon as possible.
If vision deteriorates despite these measures, surgery to reduce pressure within the skull may be needed and may be able to save vision. Procedures include
In optic nerve sheath fenestration, slits are cut in the covering of the optic nerve behind the eyeball. These slits allow cerebrospinal fluid to escape into the tissues around the eye, where the fluid is absorbed.
A shunt is a permanent drain made of plastic tubing. It can be surgically placed so that excess cerebrospinal fluid can be removed. The shunt is placed in the spaces within the brain or in the space just below the spinal cord in the lower back. The tubing is run under the skin, usually to the abdomen, where excess fluid can drain.
Stenting involves placing a wire mesh tube (stent) in a narrowed venous sinus to widen it.
If people are obese and other measures are ineffective, surgery to help with weight reduction (bariatric surgery, such as a gastric bypass) may be done. If successful, it may cure the disorder.