Idiopathic Intracranial Hypertension (IIH) is a neurological condition of unknown cause defined by increased intracranial pressure (ICP) around the brain without the presence of tumour or disease.
The space around the brain is filled with water like fluid (Cerebrospinal Fluid - CSF). If, due to a variety of factors, the pressure around the brain rises then the space containing the fluid cannot expand. It is this excessively high CSF pressure that produces the symptoms of IIH.
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 occasionally 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.
Recent Statistics for incidence and prevalence in UK
The cause of IIH is unknown – idiopathic means "of unknown cause". IIH is a rare condition and early studies suggest that it affects one or two in every 100,000 people most of them women of childbearing age, but men and children are also affected. However, IIH is on the increase:
Adults: Although there are no precise figures because there is, as yet, no national reporting system, it is estimated that there are probably 1750 new cases per year in the UK. Since it is rare for people who get IIH to then lose the adverse symptoms completely, it is again estimated that the total number of people suffering IIH in the UK – where some level of treatment is still ongoing maybe as high as 20,000 to 30,000 and this total will rise as people are living longer.
Other known statistics are: 93% of people with IIH 2 are obese (BMI = 30), 25% of all men with IIH go blind1 – but this would probably be avoidable in almost every case if men reported problems to their opticians early - however some local ophthalmology identification procedures are inadequate due to low levels of awareness. Twice as many men with IIH go blind as women.
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. BPSU study pdf
1 from the Academic Unit of Ophthalmology at the University of Birmingham (Dr Alexandra Sinclair, PhD MRC Fellow – a specialist in IIH)
2‘Idiopathic Intracranial Hypertension: Recent concepts and develpoments. ACNR.2010; 3: 10-14
3Department of Health British Paediatrics Surveillance Unit (BPSU) Annual Report for 2009/2010 conducted by Dr Yim-Yee Matthews.