ABSTRACT
Cerebrospinal fluid (CSF) is the clear colourless fluid that bathes the brain and spinal cord acting as a fluid layer for protection of the central nervous system (CNS). The CSF is derived from plasma filtration and subsequent secretion by the choroid plexuses. In situations of raised intracranial pressure, CSF production remains relatively constant; however, CSF absorption increases thereby reducing total CSF volume. CSF flows from the lateral ventricles through the foramen of Monro into the third ventricle and from there via the aqueduct of Sylvius into the fourth ventricle. CSF normally contains a small number of cells and the total cell count is less than 5 cells/mm. An increase in cell counts suggests either an infection of the CNS or a number of pathological CNS conditions. Degenerative diseases of the CNS, such as multiple sclerosis, will generate elevated lymphocyte counts.
