What is IIH?  Read more about Diagnosis & Treatments

Idiopathic intracranial hypertension (IIH), also known as benign intracranial hypertension or pseudotumour cerebri, is a condition with an unknown cause or causes. The condition is associated with raised fluid pressure around the brain.  The fluid that cushions the brain is called cerebrospinal fluid (CSF).

It can cause disabling daily headaches and visual loss, which can be permanent. The raised brain pressure can press the nerves supplying the eye (also known as papilloedema) and this can affect vision. See our 'What is IIH' leaflet HERE

History and Terminology

IIH is also known by its earlier name: Benign Intracranial Hypertension (BIH) is little used because the condition can cause visual loss and therefore is not harmless or benign. You may also see it referred to as Pseudotumor Cerebri (PTC) because some sufferers present with signs and symptoms of a brain tumour despite no tumour being present, ('pseudo' meaning false).

The precise medical definition of IIH changes over time as more becomes known about it. The American Neurosurgeon Dandy defined the initial criteria for IIH before the Second World War. This criteria has been enhanced and is now called the Modified Dandy Criteria.

The pressure-volume relationship between ICP, volume of CSF, blood, and brain tissue, and cerebral perfusion pressure (CPP) is known as the Monro-Kellie doctrine or the Monro-Kellie hypothesis.

The Monro-Kellie hypothesis states that the cranial compartment is incompressible, and the volume inside the cranium is a fixed volume. Any unwanted increase in CSF pressure therefore presses upon the brain, eyes and tissues inside the skull.

Statistics for incidence and prevalence in UK

Adults:  What is the difference between incidence and prevalence?

Incidence relates to new cases of IIH in the population in a year whereas prevalence tells us how widespread it is across the whole population. Annual incidence of IIH in female patients increased from 2.5 per 100,000 person-years in 2005 to 9.3 per 100,000 person-years in 2017.1  The prevalence rate of  IIH in female patients increased from 26 per 100,000 in 2005 to 79 per 100,000 in 2017.1  

When analysed further incidence was highest in the 20 to 29 year age group (16.5 per 100 000 person-years) followed by the 13 to 19 year age group (8.7 per 100 000 person-years) and the 30 to 39 year age group (8.4 per 100 000 person-years) 1  IIH is increasing in line with increasing BMI. 

A research project 'The IIH Life' registry has been set up by the University of Birmingham. It is planned that the registry will include 40 neurological hospitals across the UK as well as health care institutions in Denmark. The registry plans to progressively expand to other European sites. 

Other known statistics are: 93% of people with IIH are obese (BMI = 30) and 25% of people with IIH have permanent severe visual loss 

Children: It is thought that there are 57 new cases of children aged 1 to 16 with IIH each year3 and the total number of children with IIH is in excess of 800. They suffer broken educations and their siblings are adversely affected spending non-school time with parents visiting hospital. There is no difference in the rate of IIH by gender in children but 50% of female children seen in 2011 were obese.

1. https://jamanetwork.com/journals/jamaneurology/fullarticle/2737044

2. from the Academic Unit of Ophthalmology at the University of Birmingham. (Prof Alexandra Sinclair, PhD MRC Fellow - a specialist in IIH)

3 http://eprints.nottingham.ac.uk/50837/8/Matthews_et_al


IIH UK is members of the following organisations.

  Genetic Alliance Logo    Neurological Alliance Logo     JLA Logo    Alliance    ;NCVO Logo    RDD Logo