Idiopathic intracranial hypertension (IIH) is a syndrome of increased intracranial pressure (ICP) without either underlying hydrocephalus or mass lesion and with normal cerebrospinal fluid (CSF) analysis.

IIH

Pseudotumor cerebri

Benign intracranial hypertension

• 90% of affected persons are women of childbearing age with elevated body mass index (BMI).

• The exact etiology remains unknown.
• Proposed pathophysiologic mechanisms underlying the raised ICP include increased brain water content, excess CSF production, reduced CSF absorption, and increased cerebral venous pressure either alone or in combination.
• Another proposed mechanism includes abnormal vitamin A metabolism leading to increased CSF retinol levels and decreased CSF absorption at the arachnoid granulations.

• IIH is a diagnosis of exclusion and criteria listed previously must be satisfied.
• Papilledema is a term often used interchangeably to refer to both optic disc edema resulting from inflammatory causes and papilledema due to increased ICP. On fundoscopic examination, the two may be indistinguishable. However, the ICP is not elevated in optic disc edema, and the pattern of vision loss differs. In optic disc edema, central vision and color vision are affected prominently as compared to papilledema due to elevated ICP, which starts with peripheral visual field constriction with enlargement of physiologic blind spot and only later leads to loss of central vision. Space-occupying lesions such as tumors, abscesses, hematoma; venous sinus thrombosis; carcinomatous meningitis; chronic meningitides such as neurosarcoidosis, central nervous system (CNS) lupus, neurosyphilis, cryptococcal meningitis, and tuberculous meningitis can all raise intracranial pressure and result in papilledema.

• Neuroimaging studies: MRI of brain with MR head venogram (MRV) computed tomography (CT) head and CT head venogram (CTV) when MRI of brain cannot be obtained. Whereas the CT/CTV requires use of contrast, the MRI and MRV do not require intravenous contrast and are thus the imaging modalities of choice in women who are pregnant. MRI/MRV without contrast does not pose a risk of harm to either the mother or fetus.
• Lumbar puncture: CSF opening pressure should be obtained in the lateral decubitus position with the legs stretched and patient relaxed. Diagnosis is confirmed by a CSF opening pressure >250 mm H₂O with normal fluid composition.
• Ophthalmologic examination: All patients with IIH need an ophthalmologic examination, including visual fields at baseline and follow-up visits. Enlargement of the blind spot and reduction in peripheral fields are commonly seen.

CSF analysis shows normal protein, glucose, and cell count.

MRI of the brain to rule out underlying structural lesions

1. 1. Absence of specific causes of raised ICP listed previously
   2. Empty sella sign often associated with chronic raised ICP but not pathognomonic
2. MR or CT venography to exclude cortical venous thrombosis
   1. May show transverse sinus stenosis without thrombosis in IIH. Absence of specific causes of raised ICP listed previously
3. CT head
   1. May show slit-like ventricles

• Treatment is aimed primarily at preservation of vision
• Weight loss in obese patients
• Continuous positive airway pressure if obstructive sleep apnea is suspected

• Acetazolamide 250 mg to 4 g/day: Reduces CSF production by inhibition of carbonic anhydrase, occasionally causing anorexia and resultant weight loss. Dose can be increased to a maximum of 4 g/day in resistant cases with visual loss.
• Furosemide 40 to 120 mg/day in divided doses: Apparent mechanism of action is by reduced sodium transport, leading to decreased total CSF volume.
• Topiramate 100 to 400 mg/day: Reported to be effective in treatment of IIH. It is a weak carbonic anhydrase inhibitor with weight loss as one of its primary side effects.
• Serial lumbar punctures (LP): SHOULD NOT BE CONSIDERED AS STANDARD TREATMENT OF IIH. LP should be attempted in patients with severe headaches resistant to medical therapy. Goal is to reduce spinal fluid pressure to allow immediate reduction in headache severity. This treatment should be reserved for the most resistant cases and should be used as a conduit to future surgical intervention. Serial LP should not be used as treatment for IIH with progressive visual loss.

Surgical intervention is indicated in cases of treatment failure and progressive visual loss.

• Optic nerve fenestration: Preferred for patients with visual loss and easily controlled headaches. Proposed mechanism is decompression of the optic nerve. Highly effective; however, has been associated with significant number of failure rates.
• CSF shunting: Neurosurgical procedure; performed in patients with significant visual deterioration and difficult-to-control headaches. Provides rapid improvement in symptoms; however, reported to have significant rates of shunt revisions because of shunt malfunction.

• IIH is a potentially blinding condition, with severe vision loss in 5% to 10% of patients; patients should be comanaged by neurologists and ophthalmologists (preferably by a neuro-ophthalmologist). Very frequent follow-up is essential until visual fields stabilize. More frequent follow-up is needed in patients with severe papilledema or visual loss at presentation.
• All patients with IIH should undergo MR or CT venography to rule out the possibility of venous sinus thrombosis.

• Neuro-ophthalmology for serial evaluation of visual fields and fundus photographs
• Nutritionist for weight loss
• General neurologist for the initial workup and eventual treatment of raised ICP

• IIH is a potentially blinding condition.
• IIH is a diagnosis of exclusion.
• IIH is a disease of young obese women of childbearing age (90% of affected patients).

Maintenance of ideal body weight is one of the best preventive mechanisms for avoidance of IIH. However, it does occur in patients with normal body weight. In these cases, consider offending medications. However, there may be no known preventable risk factors.

The combination of weight loss and medical therapy is highly effective in treatment of IIH. Given that most patients with IIH are young and otherwise healthy, high success rates can be accomplished.

Diplopia (Section II, Differential Diagnosis)

Optic Atrophy (Related Key Topic)