The CSF space is a dynamic pressure system. Reduction of the CSF turnover rate during ageing leads to accumulation of catabolites in the brain and CSF that are also observed in certain neurodegenerative diseases. CSF is renewed about four times every 24 hours.
Experimental data suggest that cranial and spinal nerve sheaths, the cribriform plate and the adventitia of cerebral arteries constitute substantial pathways of CSF drainage into the lymphatic outflow system. Cranial and spinal arachnoid villi have been considered for a long time to be the predominant sites of CSF absorption into the venous outflow system. Additional factors such as respiratory waves, the subject's posture, jugular venous pressure and physical effort also modulate CSF flow dynamics and pressure. CSF circulation from sites of secretion to sites of absorption largely depends on the arterial pulse wave. Brain interstitial fluid, ependyma and capillaries may also play a poorly defined role in CSF secretion.
CSF is predominantly, but not exclusively, secreted by the choroid plexuses. The mean CSF volume is 150 ml, with 25 ml in the ventricles and 125 ml in subarachnoid spaces. The cerebrospinal fluid (CSF) is contained in the brain ventricles and the cranial and spinal subarachnoid spaces.
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