The ﬂuid within the ventricles of the brain and bathing its surface and that of the spinal cord. Normally a clear, colourless ﬂuid, its pressure when an individual is lying on one side is 50 to 150 mm water. A LUMBAR PUNCTURE should not be done if the intracranial pressure is raised (see HYDROCEPHALUS).
The cerebrospinal ﬂuid (CSF) provides useful information in various conditions and is invaluable in the diagnosis of acute and chronic inﬂammatory diseases of the nervous system. Bacterial MENINGITIS results in a large increase in the number of polymorphonuclear LEUCOCYTES, while a marked lymphocytosis is seen in viral meningitis and ENCEPHALITIS, tuberculous meningitis and neurosyphilis. The total protein content is raised in many neurological diseases, being particularly high with neuroﬁbromatosis (see VON RECKLINGHAUSEN’S DISEASE) and Guillan-Barré syndrome, while the immunoglobulin G fraction is raised in MULTIPLE SCLEROSIS (MS), neurosyphilis, and connective-tissue disorders. The glucose content is raised in diabetes (see DIABETES MELLITUS), but may be very low in bacterial meningitis, when appropriately stained smears or cultures often deﬁne the infecting organism. The CSF can also be used to measure immune proteins produced in response to infection, helping diagnosis in cases where the organism is not grown in the laboratory culture.