Idiopathic intracranial hypertension (IIH)

Idiopathic intracranial hypertension (IIH)

What is idiopathic intracranial hypertension (IIH)?

Idiopathic intracranial hypertension (IIH), is a neurological condition, characterized by increased intracranial pressure. Sometimes it is referred to as benign intracranial hypertension (IIH) or pseudotumor cerebri. It is regarded as “idiopathic” since the cause is not usually identified and is not always “benign”, as it may lead to blindness. The word pseudotumor indicates that it presented with symptoms similar to that seen with brain tumours in the past but without any tumour present. The cerebrospinal fluid (CSF) pressure, when measured, is usually raised.

Idiopathic intracranial hypertension
Overweight young females  with pulsating tinnitus and blurred vision may be suffering from idiopathic intracranial hypertension (IIH).

How common is it?

IIH occurs in about 1 per 100 000 of the population. It is most commonly seen in younger females with obesity a powerful predictor. It can rarely occur in children.

What is the mechanism of idiopathic intracranial hypertension (IIH)?

Three possible mechanisms may contribute to the formation of IIH. The following may occur in isolation or combination:

  • An increase in the cerebrospinal fluid (CSF) pressure
  • An increase in the intracranial blood volume or brain tissue
  • A reduction in the intracranial venous blood drainage

What may cause idiopathic intracranial hypertension (IIH)?

The specific cause is unknown, and the diagnosis of IIH can only be made if the symptoms are not better attributed to another disorder. Systemic lupus erythematosus (SLE), chronic sick kidneys, and sleep apnoea are medical conditions that may cause an increase in intracranial pressure and should be kept in mind.

Although rare, certain medications may also increase intracranial pressure. These include the contraceptive pill, high doses of vitamin A and long-term tetracycline antibiotic therapy.

Venous sinus stenosis is the narrowing of the venous sinuses in the skull. It is an under-diagnosed condition and cause of pulsatile tinnitus. There is an association between IIH and venous sinus stenosis.

The clinical picture of idiopathic intracranial hypertension (IIH).

Patients often present to the ear-nose-and-throat (ENT) surgeon with the complaint of pulsatile tinnitus. Pulsatile tinnitus beats in synchrony with the heartbeat. The most common symptom is a throbbing headache, usually worse in the morning. It is most often generalized and may lead to nausea and vomiting. Increasing the intracranial pressure as with sneezing and coughing typically aggravate the headache. Double vision and visual disturbances due to pressure on the nerves and even loss of vision can occur. A fundoscopy (eye examination) will usually be ordered.

Other neurological symptoms may include facial nerve weakness, general weakness, numbness, incoordination, and loss of smell (anosmia).

Affected females are often overweight.

How is it diagnosed?

Brain imaging with computed tomography (CT) or preferably magnetic resonance imaging (MRI) is the investigation of choice. It is primarily performed to exclude mass lesions of the brain. Although usually normal in IIH, it may show a small slitlike ventricle, buckling of the optic nerves, and other subtle abnormalities.

The eyes are examined through a fundoscopy to identify optic nerve pressure (papilledema). Blockage and narrowing of cerebral venous sinus which may occur with thrombosis results in a reduction in intracranial venous blood drainage and may be demonstrated with MR venography or cerebral catheter venography.

Lumbar puncture (LP) may show a high opening cerebrospinal fluid pressure but may also be normal. The constitution of the CSF should be normal. Removing some fluid may transiently improve symptoms.

The treatment of idiopathic intracranial hypertension (IIH).

Medical treatment includes diuretics such as acetazolamide which reduces CSF formation and pain killers that may help for headaches.

Surgical options include decompression surgery of the optic nerves to preserve vision and the placement of shunts to drain CSF.

The main aim of treatment is to prevent blindness and improve symptoms. Lumbar puncture with the removal of cerebrospinal fluid, relieves the pressure, improving the symptoms, and may even be curative. In some cases, LP has to be repeated as symptoms may recur. Weight loss is advisable.

Medical treatment includes diuretics such as acetazolamide which reduces CSF formation and pain killers that may help headaches. Surgical options include decompression surgery of the optic nerves to preserve vision and shunts’ placement to drain CSF.

Venous sinus stenosis of the transverse sinus may benefit from the placement of a permanent stent.