Glossary term:

Spontaneous intracranial hypotension

A rare condition in which cerebrospinal fluid leaks, spontaneously, from the theca which lines the spinal canal. The fluid that drains out of the spine and the head causes the brain to lose buoyancy. The brain slumps downwards and pulls on the arteries that supply it with blood. It also presses on the membranes that line the skull. These structures contain nerve fibres which then send pain signals to the brain itself and which are perceived as headaches. The headaches of spontaneous intracranial hypertension characteristically develop or are made worse when the affected individual is upright for a period and are relieved by lying down. In this respect they are similar to the low-pressure headaches that develop after a lumbar puncture.