Idiopathic Intracranial Hypertension | Simple Revision Notes for Medical Students

If you break down the name of the condition, IIH involves raised intracranial pressure with no identifiable cause (idiopathic).
The precise aetiology is still not known but several theories exist on the cause.
One example is a proposition of transverse venous sinus stenosis. The intracranial venous sinuses are responsible for CSF drainage, so a proposed mechanism is stenosis of the transverse sinus ultimately results in reduced CSF reabsorption and thus higher pressures.
Other theories do exist such as abnormalities in vitamin A metabolism or the presence of microthrombi in cerebral veins.

Female sex and obesity: IIH most commonly affects young, obese women.
Sleep apnoea
Polycystic ovarian syndrome
Association with certain drugs including isotretinoin (Roaccutane), tetraycyclines and nitrofurantoin

Headache:
- Usually bilateral
- May be worsened by coughing/sneezing/straining.
- Can be described as being worse in the mornings
- Can be worsened by lying down/bending forward and relieved by standing up
Pulsatile tinnitus
Visual disturbances
- Transient vision loss, particularly when bending down
- Bilateral papilledema
- Diplopia
- Decreased visual acuity
- Painful eye movements
- 6th nerve palsy
- Peripheral vision loss
Pain in the back or neck

Based on the clinical history, it is important to rule out any other causes of raised intracranial pressure prior to making a diagnosis of IIH.

Bedside

History & Examination (Particularly cranial nerves, upper limb neurological and lower limb neurological)
Fundoscopy: Visualise papilledema
Lumbar puncture: Typically shows a raised opening pressure (>25cm3) but is otherwise normal. Lumbar punctures may also be therapeutic.

Imaging

CT or MRI: No obvious lesions should be identified on CT/MRI i.e. by definition; an intracranial mass cannot be responsible for IIH as IIH is characterised by being idiopathic. The empty sella sign may be visualised, which is a flattened pituitary gland, occurring as a result of increased pressure
CT or MRI venogram: To exclude venous sinus thrombosis

Special Tests

Conservative

Advise weight reduction – may be able to involve dietetics to facilitate this

Medical

Acetazolamide: This is a carbonic anhydrase inhibitor. It is an effective drug used to lower intracranial pressure as it reduces CSF production. Can be poorly tolerated due to side effects:
- Paraesthesia, particularly in the extremities
- Tinnitus
- Lethargy
- Altered taste
Topiramate: Used as an alternative to acetazolamide as it has weak carbonic anhydrase properties.

Surgical

Lumbo-peritoneal or ventriculo-peritoneal shunting: Shunting CSF into the abdomen either from the lumbar spine or from the ventricle
Optic nerve sheath fenestration: Creating opening in the sheath of the optic nerve to help relieve pressure from the nerve and protect against visual field loss.

Neurology Revision Notes