Benign intracranial hypertension
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Benign intracranial hypertension (BIH), more properly called idiopathic intracranial hypertension (IIH), and previously known as pseudotumor cerebri (PTC) is a neurologic disease that is caused by increased intracranial pressure of the cerebrospinal fluid (CSF) in the subarachnoid space surrounding the brain without radiological indication of intracranial pathology. This pressure increase is theoretically due to either overproduction (by choroid plexus cells), by blockage of CSF flow, or by poor absorption of CSF. Blockage of CSF flow is termed hydrocephalus and is an acute disaster. Overproduction of CSF is at most remarkably rare. So PTC is usually related to poor CSF absoption.
Pseudotumor cerebri syndrome reflects a known cause. For example, vitamin A, or clots in the veins that drain the brain can cause a back up in CSF absorbtion. When the pathology is less clear, the diagnosis is that of idiopathic pseudotumor cerebri, or just simply PTC. Both the terms "benign" and "pseudotumor" are used to denote the fact that brain tumors frequently cause a raised ICP. As both terms are potentially misleading ("benign" also denotes "causing little harm", while IIH may cause severe complications), IIH is now favored.
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Signs and symptoms
PTC commonly affects women between ages 20 and 50. Symptoms are severe headache and vomiting, nausea, transient visual obscurations, double vision, and, most concerning, permanent loss of visual field and then all vision. Additional symptoms vary. The name of the disease comes from the fact that these symptoms are also frequently observed in patients with brain tumor, and the elevated pressure of the CSF on the optic nerves creates papilledema, which also occurs with brain tumors. Risk factors are overweight, use of the oral contraceptive pill and various types of medication (including tetracycline antibiotics and vitamin A).
Diagnosis
The diagnosis of PTC is one of exclusion. However, the so-called modified Dandy criteria usually need to be met. For the diagnosis of PTC, there should be papilledema, there should not be any structural abnormality of the brain in neuroimaging, and the lumbar puncture should confirm a high pressure in the absence of other abnormalities (like meningitis). Due to the possibility of causing a brain herniation if an actual tumor is present, a lumbar puncture (spinal tap) should only be performed after a negative MRI or CT scan. Abnormal high pressure with exclusion of other causation is considered a defintive diagnosis.
Treatment
The main concern in treatment is preventing visual loss. Elevated CSF levels put pressure on the optic nerves as it does all of the brain. However, the optic nerve head undergoes asymmetric pressure (from behind but not from in front) and this leads to bulging of the optic disc. When billateral, this is termed papilledema, and if it is extensive enough and for enough time it proceeds from mild visual disturbances to complete blindness. Prevention of vision loss is a primary concern in treatment.
The treatment of pseudotumor cerebri is to remove the inciting cause, if possible, and reduce the CSF pressure. Pseudotumor cerebri may resolve after initial treatment, may not resolve for years, or may resolve and return chronically.
Pressure may be decreased by repeated spinal taps (to remove excessive cerebrospinal fluid), drugs that reduce cerebrospinal fluid production (acetazolamide, Diamox®) or diuretics. Diamox is the most common CSF inhibitor used in treatment; it can cause drowsiness and hypokalemia. Depending on severity there are other treatment options available, such as optic nerve sheath fenestration, and shunts to remove excess CSF from the brain.
Shunting is a neurosurgical procedure to facilitate the draining of excess CSF to the normal circulation. There are various types of shunting operations; lumboperitoneal shunts drain from the lumbar spine to the peritoneal cavity, while ventriculoatrial shunts run from the cerebral ventricles to the heart. Although shunts can dysfunction due to occlusion or compression, they are very effective in normalizing CSF pressures. Optic nerve sheath fenestration, is may be less effective in controlling the CSF pressure (and hence most of the symptoms such as headache), but is more effective in protecting the nerve from the effects of pressure. Hence, in cases of severe visual loss, it is often the procedure of choice.
External links
- Intracranial Hypertension Research Foundation (http://www.ihrfoundation.org/)