What is Idiopathic Intracranial Hypertension?
Idiopathic intracranial hypertension or IIH is a neurologic disorder characterized by elevation of the intracranial pressure (ICP). The cranium is a closed system, and any increase in pressure beyond normal limits inside the cranium will lead to compression and damage of brain tissue.
The intracranial pressure is maintained by efficient blood flow and the production and reabsorption of cerebrospinal fluid (CSF).
The disorder was originally termed as pseudotumor cerebri (PTC) because it mimics a brain tumor although no tumor is present. Due to the absence of malignancy, it was then changed to benign intracranial hypertension (BIH). However, because the condition can be neither a benign case nor a false tumour and because the condition may result in blindness, the term was changed to idiopathic intracranial hypertension.
IIH occurs is one in every 100,000 people, and it is more apparent in women than in men. There is no difference in the rate of IIH by gender in children.
Signs and Symptoms
IIH produces signs and symptoms that result from the elevation of the ICP. These arise within hours to weeks of intracranial elevation. The most common symptom is the headache.
- Headache - Headaches, characterized as throbbing and generalized, occur in almost all the patients with IIH. The pain or discomfort can radiate to the shoulders and neck. It is more severe in the morning and may worsen during coughing and sneezing because of further increase in the ICP.
- Pulsatile Tinnitus - Tinnitus (ringing in the ears) may also be experienced as a result of increased pressure in the otic nerve.
- Projectile Vomiting – An increase in the ICP can lead to projectile vomiting. When the ICP put pressure on the vomiting center in the brain, the severe compression causes vomiting.
- Lack of coordination and unstable balance – An increased ICP may also cause compression of the cerebellum, which is responsible for balance and coordination.
- Double vision - The abducens nerve may also be affected, leading to abducens nerve palsy.
- Facial muscle weakness and transient loss of senses - Other cranial nerves may also be affected with the increased ICP, leading to problems in facial expressions and the interpretation of senses.
- Visual obscurations - Visual obscurations involve the presence of blind spots in the vision as a result of papilledema (swelling of the optic disc).
The exact cause of the condition is unknown because the usual findings in diagnostic tests do not indicate any underlying conditions. However, obesity may contribute to the development of IIH. If other underlying conditions which cause an increased ICP are present, then the diagnosis of secondary intracranial hypertension is made.
Any increase in the ICP is associated with the increased volume of brain tissue, cerebrospinal fluid (CSF), and blood, the three most common components of the cranium.
Any increase in brain tissue (ex., presence of tumor) may lead to an increased ICP. Cerebral edema (swelling of the brain) may also occur as a result of infection and other conditions. However, with IIH, there is an absence of these conditions.
The blood may also be a cause of the increased ICP. Any obstruction in the venous blood flow leads to blood congestion in the cranium. In addition, the CSF may also be a factor in the elevation of the ICP. Poor reabsorption of CSF by the ventricles leads to an increased amount of CSF circulating through the Central Nervous System (CNS).
Diagnostic tests of IIH include:
Imaging tests involving the brain is essential in identifying any underlying conditions. Imaging tests may include MRI or CT scan. Normal brain scan results indicate that there are no underlying conditions involving the brain that may cause the increased ICP. Venogram of the intracranial veins may also be undertaken to identify the presence of cerebral venous sinus thrombosis (CVST).
Lumbar puncture is employed to determine any abnormalities and cytologic changes in the CNS that may cause an ICP increase. Infections of the CNS and presence of tumors may be detected using analysis of the CSF. Lumbar puncture also measures the opening pressure in the CSF, thereby identifying the increased ICP.
The diagnosis of IIH is made based on the modified Dandy criteria, described as the following:
- Elevated ICP symptoms
- Normal findings on brain scan
- Absence of localizing signs
- No alteration in level of consciousness (i.e., patient is alert and awake)
- Normal cytologic findings in lumbar puncture with an increased ICP of more than 25 cm H20.
- Absence of any other reasons for the increased ICP.
Treatment of IIH is primarily geared towards the normalization of the ICP since no other conditions can be treated to eradicate IIH. Treatments are also done to reduce pressure in the optic disc and to prevent permanent vision loss. Treatments include:
Diuretic medications are administered to reduce the ICP by inhibiting further production of CSF. This also allows the kidneys to excrete excess fluid from the body. Diuretics which are used are in the form of carbonic anhydrase inhibitors such as acetazolamide (Diamox) or loop diuretics such as furosemide.
Analgesics such as ibuprofen and acetaminophen can be used to relieve headaches.
Corticosteroids such as methylprednisolone are also given to reduce cerebral edema. This significantly causes reduction in ICP. However, the dose of corticosteroids should be tapered accordingly to prevent rebound edema once the medication is discontinued.
Lumbar puncture is employed to directly reduce the ICP by removing some CSF. The lumbar puncture is done by inserting a thin needle on the spine and then aspirating the CSF. Lumbar puncture is also an emergency procedure to prevent vision loss when visual obscurations are already apparent.
Surgery ,which involves the creation of shunts from the ventricles to effectively drain the CSF, is done when patients do not respond to lumbar puncture and other treatments. Ventriculoperitoneal shunt is employed to create a shunt from the ventricles into the peritoneum so that the CSF can be absorbed in the circulation and eliminated through the urine. Optic nerve sheath decompression may also be done to prevent permanent loss of vision.
The treatment for the increased ICP should be immediately employed to prevent complications. Patients usually respond to treatment, but some may experience chronic IIH and eventually some of its complications.
The primary complication of IIH is the presence of papilledema. Papilledema can result in vision loss when untreated.
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