Idiopathic intracranial hypertension

Idiopathic intracranial hypertension (IIH) (also known as benign intracranial hypertension or pseudotumour cerebri) is a syndrome of signs and symptoms of increased intracranial pressure without causative mass or hydrocephalus identified.

Epidemiology

Typical demographics involves middle aged obese females.

Clinical presentation

Presentation is usually with headaches, visual problems and papilloedema. Papilloedema may not always be present, or may be unilateral, making the clinical diagnosis less than straightforward ⁶. Neurological examination is usually normal, with a sixth cranial nerve palsy sometimes encountered.

Additional clinical findings include normal CSF composition with elevated opening pressure (opening pressure varies however, with a mean pressure of less the 35mmHg, with pressure waves as high as 80mmHg which last 5 to 20 minutes) ⁶.

Pathophysiology

Idiopathic intracranial hypertension (IIH) is a poorly understood condition. Various mechanisms have been proposed to explain the pathogenesis of BIH, including decreased cerebrospinal fluid (CSF) absorption, increased CSF production, increased intravascular volume, and increased intracranial venous pressure.¹  

Associations

A variety of conditions are known to be associated with IIH including:

• endocrine
  • adrenal insufficiency
  • Cushing disease
  • hypoparathyroidism
  • hypothyroidism
  • excessive thyroxine replacement in children
• drugs
  • doxycycline ²
• chronic renal failure
• systemic lupus erythematosus (SLE)
• hypervitaminosis A (in the pediatric population)

Radiographic features

CT / MRI

Imaging of the brain with CT and MRI is essential in patients IIH, to exclude elevated CSF pressure due to brain tumour, dural sinus thrombosis, hydrocephalus etc...

Features that support the diagnosis include ^3,6:

• slit like ventricles
• optic nerves
  • prominent subarachnoid space around the optic nerves : ~ 45%
  • papilloedema (flattening of the posterior sclera) seen in : ~ 80%
  • vertical tortuosity of the optic nerves : ~ 40%
  • enhancement of the prelaminar optic nerves : ~ 50%
• partial empty sella turcica : ~ 70%
• dural venous sinus flow decreased and compressed sinuses : assessed on CTV / MRV

These changes may be reversible ³

Treatment and prognosis

Treatment options include CSF letting, acetazolamide and lumboperitoneal shunts. In patients with progressive visual deterioration optic nerve fenestration to preserve vision.

Venous sinus stenting has also been tried ⁴ although it is controversial as to whether apparent venous sinus stenosis is the cause or the effect of IIH. Spontanous resolution of apparent stenosis is certainly recognised ⁶.

Differential diagnosis

Other causes of raised ICP and papilloedema should be sought, including:

• mass
• dural venous sinus thrombosis
• hydrocephalus etc...