CSF Flow dynamics
Most of the CSF is formed by the choroid plexus of the ventricles at a rate of about 0.35 cc/min or 20 cc/h or 500 cc/day, which is three to four times as much as the total volume of entire CSF. The ependymal surfaces of the ventricles and the arachnoid membranes also produce small amounts. The red arrows in Figure 1 shows the main channels of CSF flow. The CSF secreted in the lateral ventricles passes first into the third ventricle, then it flows downward through the aqueduct of sylvius into the fourth ventricle. Finally, the fluid passes out of the fourth ventricle through the foramen of Luschka and Magendie, entering the cisterna magna. Almost all the CSF then flows upward from the cisterna magna through the subarachnoid spaces. From there it is absorbed into the venous sinuses through the arachnoidal villi and finally returned to the systemic circulation (Figure 1). The 10- 15 cc of CSF that is collected during an LP procedure, is replenished in about half an hour in a healthy normally hydrated patient.2