This article waslast modified on
10 July 2017.
Normally clear liquid, produced in the ventricles of the brain, that fills and protects the cavities in the brain and spinal cord. In the adult there is normally about 140 millilitres of cerebrospinal fluid. Samples of the fluid, obtained by lumbar puncture (taking CSF from the bottom of the spine using a special syringe), may be used to diagnose certain diseases.