Idiopathic Intracranial Hypertension 

The presentation of a patient with symptoms of increased intracranial pressure and papilledema should be considered a clinical emergency until neuroimaging study results confirm the presence or absence of an intracranial mass.

A significant number of patients presenting in the above fashion whose neuroimaging study results do not reveal a mass lesion are diagnosed with idiopathic intracranial hypertension. Although idiopathic intracranial hypertension, pseudotumor cerebri, and benign intracranial hypertension are synonymous with this diagnosis, the preferred term is idiopathic intracranial hypertension.

The diagnostic criteria, including those of the modified Dandy criteria as described by Dandy in 1937 and later modified by Smith in 1985, are as follows: there are symptoms and signs of increased intracranial pressure; there are no localizing neurologic signs (with the exception of a unilateral or bilateral sixth nerve paresis); cerebrospinal fluid can show increased pressure, but there are no cytologic or chemical abnormalities; and normal to small symmetric ventricles must be demonstrated. Subsequent additions to these criteria include the following: the diagnostic lumbar puncture should be in the lateral decubitus position; MRI/venography should be included to rule out intracranial venous sinus thromboses; and other causes of intracranial hypertension should be ruled out.^{[1, 2, 3]}

The pathophysiology of this disorder is unclear. A relative resistance to the absorption of cerebrospinal fluid across the arachnoid villi is widely presumed to be present. Other theories support an abnormality in the cerebral circulation with a resulting increase in the brain's water content. The subsequent increase in the intracranial pressure is transmitted to the structures within the intracranial cavity, including the optic nerves. Unfortunately, because of the difficulty in applying animal models of cerebrospinal fluid dynamics to humans, the underlying pathophysiology in idiopathic intracranial hypertension remains unclear.

Current hypotheses include the link between relatively obstructive segments in the distal transverse sinus and idiopathic intracranial hypertension or the presence of increased arterial inflow with an accompanying low-grade stenosis of the transverse sinus.^{[4, 5]}

The disease commonly occurs in women who are overweight. The role of obesity in this disorder is unclear. In some instances, obesity and idiopathic intracranial hypertension may be familial.^[6] Obesity has been proposed to increase intra-abdominal pressure, which, in turn, raises cardiac filling pressures. This rise in pressure leads to impeded venous return from the brain (due to the valveless venous system that exists from the brain to the heart) with a subsequent elevation in intracranial venous pressure. If not treated appropriately, chronic interruption of the axoplasmic flow of the optic nerves with ensuing papilledema due to this pressure may lead to irreversible optic neuropathy.^[7]

Frequency

United States

Studies of American-based populations have estimated that the incidence of idiopathic intracranial hypertension ranges from 0.9-1.0 per 100,000 in the general population. This incidence rate increases to 1.6-3.5 per 100,000 in women and to 7.9-20 per 100,000 in women who are overweight.^{[1, 3, 5]}

International

The incidence of idiopathic intracranial hypertension is variable from country to country. Because of the relation of the disease to body habitus, its occurrence varies according to the incidence of obesity in the respective region.

Mortality/Morbidity

• The morbidity of this disorder is mainly related to the effects of papilledema on visual function.^[8]
• If left untreated, long-standing disc edema results in an irreversible optic neuropathy with accompanying constriction of the visual field and loss of color vision.^{[9, 10]}
• In end-stage papilledema, central visual acuity is also involved.

Sex

A strong predilection of this disease exists for women. More than 90% of patients with idiopathic intracranial hypertension are women of childbearing age.^[5] However, men with idiopathic intracranial hypertension are twice as likely as women to lose visual function due to their papilledema. Thus, the visual function of men with idiopathic intracranial hypertension must be followed more closely to avoid irreversible damage.^[11]

Age

Although idiopathic intracranial hypertension may affect individuals of any age, most patients with this disease present in the third decade of life.^[5]

Idiopathic intracranial hypertension does occur in the pediatric population^[12] ; these younger patients are often not obese.