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Idiopathic Intracranial Hypertension

Pathogenesis and Pathophysiology. The pathophysiology of IIH is unknown. Postulated mechanisms include increased CSF production, decreased CSF absorption, and increased venous sinus pressure. Some studies suggest that interstitial brain edema and a decreased rate of absorption at the arachnoid villi are the major contributors. The disturbances of CSF hydrodynamics in IIH persist for years. Increased CSF pressure in IIH may result from a rise in venous sagittal sinus pressure secondary to extracellular edema causing venous obstruction, or from low conductance for CSF reabsorption producing a compensatory increase in CSF pressure.

Epidemiology and Risk Factors. IIH with papilledema occurs with a frequency of about one case per 100,000 per year in the general population and 19.3 cases per 100,000 per year in obese women aged 20 to 44. The patient with IIH is commonly a young, obese woman with chronic daily headaches, normal laboratory studies, an empty sella, and a normal neurological examination.

Clinical Features and Associated Disorders. The symptoms of IIH consist of generalized increased intracranial pressure, with headache occurring in most, but not all, patients. Bifrontotemporal headache is most common. Unilateral headache with increased CSF pressure due to IIH may be an exacerbation of migraine or a new local phenomenon. Transient visual obscuration, an episode of visual clouding in one or both eyes usually lasting seconds, occurs with all forms of increased intracranial pressure with papilledema but is not a specific symptom. Transient visual obscurations can occur in patients without increased intracranial pressure who have elevated optic discs from other causes. Persons without papilledema do not have transient visual obscurations. Pulsatile tinnitus, diplopia, and visual loss can occur. Some patients report shoulder and arm pain (perhaps secondary to nerve root dilatation).

IIH without papilledema has been described in some patients. The headache and demographic characteristics are identical to those of patients with papilledema except for (1) possible association with prior head trauma or meningitis; (2) extended delay in diagnosis, which requires lumbar puncture in the absence of papilledema; and, (3) no evidence of the visual loss seen in patients with IIH with papilledema.

Differential Diagnosis. IIH may be either (1) truly idiopathic, with no clear identifiable cause, or (2) symptomatic, a result of venous sinus occlusion, radical neck dissection, hypoparathyroidism, vitamin A intoxication, systemic lupus erythematosus, renal disease, or drug side effects (nalidixic acid, danocrine, steroid withdrawal).