Idiopathic intracranial hypertension

Idiopathic intracranial hypertension is raised intracranial pressure, the pressure inside the rigid skull, with no definable cause. Scans show no tumour or other mass that takes up space and no hydrocephalus (a build-up of fluid in the cavities of the brain). There is no infection, and the cerebrospinal fluid (CSF, the clear fluid around the brain) has a normal make-up. The diagnosis is made by excluding those causes.

It mainly affects women of childbearing age, and obesity is the strongest risk factor. The incidence is about 1 per 100,000 in women of normal weight but about 20 per 100,000 in women with obesity.

The typical headache is daily, constant and usually worse in the morning. Lying flat overnight reduces the drainage of venous blood (blood returning to the heart in the veins) from the brain, so the pressure builds. Bending forward or coughing makes it worse still.

Papilloedema is usually bilateral, and there may be transient visual obscurations (seconds-long greying out of vision). Permanent loss of vision is the main danger, and it may not be noticed until late, so the back of the eye is checked (fundoscopy) even when vision seems normal. Apart from sometimes a sixth cranial nerve problem that causes double vision, the rest of the neurological examination is usually normal.

The cause is not fully understood. The leading theory is impaired absorption of CSF at the arachnoid granulations (tiny projections that push into the large venous channels of the skull), where it normally returns to the blood. A lumbar puncture (a needle in the lower back to measure the CSF pressure) shows a high opening pressure after normal brain imaging. Treatment includes weight loss and acetazolamide, a drug that reduces CSF production.