The cerebrospinal fluid system (CSF) lies at the centre of the brain and extends throughout the nervous system, between the two innermost cerebral meninges. CSF is produced in the ventricles and drains from the top of the convexity in the dural venous sinuses. The function of the CSF is not entirely clear. However, it is known at least to perform a mechanical function. Analysis of the CSF for sugar, proteins, immunoglobulins, cells and other substances provides a basis for accurate diagnosis, since various conditions are associated with distinct CSF characteristics. Disorders of the CSF system can lead to hydrocephalus, intracranial hypertension and intracranial hypotension (all of which can be treated with reasonable efficacy).