The CSF formed by the choroid plexus of the ventricles circulates through the interventricular foramens into the third ventricle and then via the cerebral aqueduct into the fourth ventricle. From there the fluid passes to the subarachnoid space through some additional foramens and is then absorbed by the venous system to the blood circulation. The total amount of CSF is about 150 ml, and about 500 ml is produced everyday, which indicates its very active circulation.
CSF can be tested for the diagnosis of a variety of neurological diseases. Usually, it is obtained by a procedure called lumbar puncture in an attempt to count the cells in the fluid and to detect the levels of protein and glucose. These parameters alone may be extremely beneficial in the diagnosis of central nervous system infections (especially meningitis and subarachnoid hemorrhage). Moreover, a CSF culture examination may yield the microorganism that has caused the infection. By using more sophisticated methods as the detection of the oligoclonal bands, an ongoing inflammatory condition (for example, Multiple sclerosis) can be recognized. Lumbar puncture can also be performed to measure the intracranial pressure, which is increased in a condition known as hydrocephalus.