Idiopathic intracranial hypertension (IIH) is a condition related to chronic increase in intracranial pressure. It has also been known as Pseudotumour Cerebri (because the headaches can mimic that seen in patients with a brain tumour) and Benign Intracranial Hypertension. The term Benign Intracranial Hypertension is a misnomer as IIH can be associated with serious and irreversible consequences including loss of vision.
IIH occurs in approximately 1 in 100,000 people. It is 20 times more common in females with increased body mass index.
IIH is related to an imbalance between the production and resorption of cerebrospinal fluid, which is the colourless water-like fluid that surrounds the brain and spinal cord. The underlying mechanism of this imbalance is not clearly understood, though there is evidence to suggest hormonal and inflammation influences can alter the balance.
The most common symptom is high pressure headache, which can vary but is often throbbing or migraine-like and worse in the mornings. Other symptoms occur more variably and include visual symptoms such as double vision, blurry or reduced vision. Nausea and vomiting or tinnitus (ringing sensation in the ear) may also occur.
How is IIH diagnosed?
IIH diagnosis is based on a combination of clinical features, evidence of elevated CSF pressure and after ruling out other causes for increased pressure. Your doctor may suspect IIH if you have typical symptoms such as headaches or visual changes. In some circumstances the diagnosis is suspected after attending an optometrist or eye specialist due to a change in vision.
If IIH is suspected a brain scan is required to further assess and rule out other important causes of increased intracranial pressure (such as hydrocephalus, tumour, inflammation). CT scan may be considered in the first instance, however MRI is better. There are many signs that can suggest IIH on MRI.
Further testing is necessary, and a lumbar puncture is performed to measure the CSF pressure. This procedure involves insertion of a very small needle into the lower spine, usually only requiring local anaesthetic, in order to measure the pressure. This procedure can be performed under imaging guidance. The fluid drained can be sent for further testing, and in many cases the patient may experience some improvement in symptoms after fluid is drained (though this improvement is not long lasting as the fluid reaccumulates).
What treatments are available?
After the diagnosis of IIH has been established treatment can be instituted. The majority of patients can be effectively managed with conservative medical therapy. In cases where conservative medical treatment is not effective, surgical or endovascular treatments can be considered.
Conservative measures include weight loss and medications. Weight loss can take some time, but has been shown to be effective. Medications such as acetazolamide and topiramate can be used to alter (reduce) the CSF production and this can result in reduced CSF pressure.
In cases that are not responsive to conservative therapy, surgical or endovascular therapies may need to be considered. Common surgical therapies include optic nerve sheath fenestration and CSF diversion (lumbar or ventricular peritoneal shunt surgery). Shunt surgery can be effective but is associated with a high failure rate (up to 39%) and multiple revisions (repeat surgeries) may be required.
The endovascular treatment option is Venous Sinus Stenting (VSS).
Venous Sinus Stenting
In cases where a narrowing of the venous drainage of the brain has been identified, Venous Sinus Stenting (VSS) is a treatment option. The narrowing can usually be found on CT or MRI, though a formal catheter cerebral angiogram is the most sensitive test for this. At the same time the angiogram is performed, venous sinus manometry can be performed. This involves measuring the venous pressure through a small catheter. Identifying a large pressure change on either side of a vein narrowing is a strong indicator that stenting will be an effective intervention to reduce intracranial pressure.
In VSS a catheter is inserted into the venous sinus across the area of narrowing, and a flexible (metal alloy) tube is placed to widen the narrowing. This results in improved drainage of blood from the brain and reduced pressure.
VSS is minimally invasive, usually only requiring a small incision at the groin to access the blood vessels (and in some cases can even be performed from the arm). VSS is performed under general anaesthesia. You will be started on antithrombotic medication prior to the procedure. This procedure is very safe with reported rates of serious adverse effects (such as bleeding related to the veins) only occurring in 2% of cases. In appropriately selected patients VSS has been shown to be effective in improving vision, reducing headaches and reducing or stopping acetazolamide/topiramate.
VSS recovery is usually very quick. Typically patients can be discharged the following day. Occasionally patients may report worsening headache in the first 48-72 hours, sometimes up to 1-2 weeks.