Idiopathic Intracranial Hypertension (Pseudotumor Cerebri)

Introduction

Idiopathic intracranial hypertension (IIH) is a disorder of elevated intracranial pressure (ICP) without apparent inciting etiology. Pseudotumor cerebri (PTC) is also a commonly accepted term describing the same disorder. Many authors advocate limiting the definition of IIH to a truly idiopathic subset of PTC, as PTC encompasses a list of known nontumor conditions resulting in elevated ICP, including the following: cerebrospinal fluid (CSF) malabsorption, superior vena cava syndrome, elevated right heart pressure, venous sinus or jugular vein thrombosis, and others. Additionally, neuroradiologists often prefer the term PTC over IIH because extracranial or radiographically occult secondary etiologies are not readily evident on routine brain imaging. Benign intracranial hypertension , yet another frequently used term, should be avoided, since the disorder can result in serious clinical outcomes including vision loss.

IIH was first recognized by Heinrich Quincke in 1893 and Walker Dandy first proposed the diagnostic criteria in 1937. Since then, multiple revised diagnostic criteria have been proposed and debated in an effort to reflect the rapid evolution of advanced neuroimaging, especially magnetic resonance imaging (MRI). Before MRI, neuroimaging had a limited role to rule out intracranial masses prior to diagnostic lumbar puncture in cases of IIH. As with other primary idiopathic disorders, the diagnostic criteria and rationale remain largely clinical ( Box 18.1 ). Hence the negative imaging findings as well as the constellation of positive clinical findings are of greater importance in diagnosis than any isolated positive imaging features.

Box 18.1

Adapted from Friedman DI, Liu GT, Digre KB. Revised diagnostic criteria for the pseudotumor cerebri syndrome in adults and children. Neurology . 2013;81:1159–1165.

Criteria for Diagnosing Idiopathic Intracranial Hypertension

1.
A diagnosis of IIH is definite if the patient fulfills criteria A through E. Otherwise a probable diagnosis can be suggested.
- A.
  Papilledema.
- B.
  Normal neurologic examination except for cranial nerve abnormalities.
- C.
  Neuroimaging: normal brain parenchyma without hydrocephalus, mass, or structural lesion and no abnormal meningeal enhancement or venous sinus thrombosis on MRI/MRV or contrast-enhanced CT.
- D.
  Normal CSF composition.
- E.
  Lumbar puncture pressure above 25 cm H ₂O (>23 cm H ₂O in pediatric patients).
2.
In the absence of papilledema, a diagnosis of IIH can be made if B through E are satisfied and, in addition, the patient has a unilateral or bilateral abducens nerve palsy.
3.
In the absence of papilledema or sixth nerve palsy, a diagnosis of IIH can be suggested but not made if B through E are satisfied and, in addition, at least three of the following neuroimaging criteria are satisfied:
- •
  Empty sella
- •
  Flattening of the posterior aspect of the globes
- •
  Distention of the perioptic subarachnoid spaces with or without tortuous optic nerves
- •
  Transverse venous sinus stenosis

CSF, Cerebrospinal fluid; CT, computed tomography; MRI/MRV, magnetic resonance imaging/venography; IIH, idiopathic intracranial hypertension.

IIH is most frequently reported in obese females of childbearing age. A review of cohort studies revealed that 57% to 100% of IIH patients are obese and there is at least a two- to threefold increased prevalence in overweight females of reproductive age compared with the general population (1–3 in 100,000). By contrast, IIH in the prepubertal pediatric population does not demonstrate strong associations with obesity or female sex.

The most common presentation symptom of IIH is headache, which occurs in 90% to 94% of cases. Other common symptoms of IIH include retro-ocular pain, transient vision obscuration, pulsatile tinnitus, photopsia, and diplopia. Although less common, visual loss occurs in approximately 30% of affected patients. Papilledema and visual changes are the most common clinical examination findings of IIH (~40%). Although palsy is less frequent, patients can also present with abducens (CN 6) palsy (~10%).

Many IIH cases without visual changes are self-limiting or only require conservative management. Cases with mild visual symptoms or papilledema necessitate treatments such as acetazolamide, therapeutic lumbar puncture, or bariatric surgery. More invasive treatments are reserved for refractory cases or rapidly progressing vision loss and include optic nerve sheath fenestration (ONSF), venous sinus stenting, and ventriculoperitoneal shunt placement. As the exact pathophysiology of IIH remains elusive, these therapeutic measures yield varying degrees of success in different patient groups.

Evolution: Overview

As the name of IIH suggests, the etiology is still unknown despite many different proposals based on numerous clinical and scientific investigations. The common ground of these proposals is centered around the alteration of CSF hydrodynamics ( Fig. 18.1 ). The association between obesity and IIH is intriguing, as successful weight loss after bariatric surgery was found to treat IIH effectively. Interestingly, recent studies of long-term spaceflight astronauts demonstrate similar clinical and MRI findings of IIH.