Cerebrospinal Fluid - Amount and Constitution

Amount and Constitution

The CSF contains approximately 0.3% plasma proteins, or approximately 15 to 40 mg/dL, depending on sampling site, and it is produced at a rate of 500 ml/day. Since the subarachnoid space around the brain and spinal cord can contain only 135 to 150 ml, large amounts are drained primarily into the blood through arachnoid granulations in the superior sagittal sinus. Thus the CSF turns over about 3.7 times a day. This continuous flow into the venous system dilutes the concentration of larger, lipid-insoluble molecules penetrating the brain and CSF.

CSF pressure, as measured by lumbar puncture (LP), is 10-18 cmH₂O (8-15 mmHg or 1.1-2 kPa) with the patient lying on the side and 20-30cmH₂O (16-24 mmHg or 2.1-3.2 kPa) with the patient sitting up. In newborns, CSF pressure ranges from 8 to 10 cmH₂O (4.4–7.3 mmHg or 0.78–0.98 kPa). Most variations are due to coughing or internal compression of jugular veins in the neck. When lying down, the cerebrospinal fluid as estimated by lumbar puncture is similar to the intracranial pressure.

There are quantitative differences in the distributions of a number of proteins in the CSF. In general, globular proteins and albumin are in lower concentration in ventricular CSF compared to lumbar or cisternal fluid. The IgG index of cerebrospinal fluid is a measure of the immunoglobulin G content, and is elevated in multiple sclerosis. It is defined as IgG index = (IgG_CSF / IgG_serum ) / (albumin_CSF / albumin_serum). A cutoff value has been suggested to be 0.73, with a higher value indicating presence of multiple sclerosis.