Examination of the cerebrospinal fluid (CSF) may provide critically important diagnostic information in a number of infectious and noninfectious medical conditions. Knowledge of the normal physiology and pathophysiology of CSF production and flow is useful in interpreting such test results.
This topic will review the normal physiology and composition of CSF. The technique for obtaining CSF via lumbar puncture (LP) and the complications and contraindications to this test are discussed separately. (See "Lumbar puncture: Technique, indications, contraindications, and complications in adults".)
PHYSIOLOGY OF CSF FORMATION AND FLOW
Cerebrospinal fluid (CSF) is produced by the choroid plexus in the lateral, third, and fourth ventricles and circulates through the subarachnoid space between the arachnoid mater and the pia mater. The choroid plexus consists of projections of vessels and pia mater that protrude into the ventricular cavities as frond-like villi containing capillaries in loose connective stroma. A specialized layer of ependymal cells called the choroidal epithelium overlies these villi (figure 1).
CSF is formed in the choroid plexus by both filtration and active transport. In normal adults, the CSF volume is 125 to 150 mL; approximately 20 percent of the CSF is contained in the ventricles; the rest is contained in the subarachnoid space in the cranium and spinal cord. The normal rate of CSF production is approximately 20 mL per hour.
CSF circulates from the lateral ventricles into the third ventricle and then the fourth ventricle via the cerebral aqueduct. Thereafter, CSF passes through apertures in the fourth ventricle into the subarachnoid space at the base of the brain and then flows over the convexities of the brain and down the length of the spinal cord. The CSF is propelled along the neuroaxis by a cranio-caudal pulsatile wave induced by flow in the cerebral arteries and by the associated expansions of the vascular compartment in the cranial vault.