Diagnosis and medical management of idiopathic intracranial hypertension

Introduction

Idiopathic intracranial hypertension (IIH) is a condition defined by increased intracranial pressure without an identifiable cause and its associated symptoms, most notably headache and vision loss. With an estimated incidence of 0.9 per 100,000 in the general population, IIH is primarily observed in overweight women of childbearing age, with an incidence of 7.9 to 20 per 100,000. The diagnosis of IIH requires careful consideration of the history, examination, neuro-imaging, and CSF pressure. When possible and safe, medical management should be initiated first. However, if the clinical presentation is fulminant, or if the vision worsens despite treatment, then more invasive treatment is warranted. This chapter reviews the diagnosis and medical management of IIH.

Pathophysiology

The mechanism behind idiopathic intracranial hypertension (IIH) is not entirely understood, but there are several evolving theories linking obesity and increased intracranial pressure (ICP). Cortisol dysregulation has been implicated, with obesity being associated with elevated 11β-hydroxysteroid dehydrogenase, which is thought to affect cerebrospinal fluid (CSF) production (in addition to local cortisol availability). Sinclair et al. demonstrated reduction of global 11β-hydroxysteroid dehydrogenase after weight loss. Other theories include decreased CSF reabsorption, either via microthrombosis (in setting of chronic inflammatory states) within the dural venous sinus system or via other hormonal factors (possibly leptin regulation). A significant subset of patients appears to develop intracranial hypertension as a consequence of focal stenosis of the transverse or sigmoid cerebral venous sinuses. If the stenosis is severe enough, the venous sinus pressure will increase above the site of the stenosis. Because CSF resorption from the subarachnoid space across the arachnoid granulations into the superior sagittal sinus (SSS) depends on a pressure gradient in which the CSF pressure is slightly higher than the venous pressure, an increase in the SSS pressure therefore causes the CSF pressure to rise. This variation of intracranial hypertension is covered in more detail in Chapter 17 .

The optic nerve sheath is contiguous with the subarachnoid CSF space and thus is exposed to elevations in CSF pressure. Therefore, regardless of the cause, elevated CSF pressure leads to a constellation of symptoms that includes vision loss.

Diagnosis

Idiopathic intracranial hypertension is characterized by idiopathic elevation of ICP, with other possible causes of elevated ICP ruled out before the diagnosis. The modified Dandy criteria is a set of diagnostic criteria designed to guide the diagnosis of IIH and serves as an outline for this chapter, listed in Table 16.1 . To complete the evaluation of a patient with suspected IIH, the following diagnostic workup must be completed ( Table 16.2 ).