Cerebrospinal fluid: CSF. A watery fluid, continuously produced and absorbed, which flows in the ventricles (cavities) within the brain and around the surface of the brain and spinal cord.

The CSF is produced by the choroid plexus, a series of infolded blood vessels projecting into the cerebral ventricles, and it is absorbed into the venous system.

If production exceedes absorption, the CSF pressure rises and the result is hydrocephalus. This can also occur if the CSF pathways are obstructed and CSF accumulates.