Cerebrospinal fluid circulation: Tradition and new insights

Abstract

The classic model of cerebrospinal fluid (CSF) formation, transport across the central nervous system, and absorption is based on the circulation theory. This model, where CSF is thought to be secreted by the choroid plexus, and to circulate from the ventricles into the cisterns and the subarachnoid spaces (SAS), is no longer considered reliable. Several studies indicate that CSF can be produced and absorbed throughout the entire CSF system, notably the ependyma, the perineural SAS, and the Virchow-Robin spaces (VRS). The discovery of the expression of aquaporin 1 (AQP1) in the choroidal plexus and aquaporin 4 (AQP4) in the end-feet of astrocytes underlying pia mater, has shed new light into the mechanisms of fluid exchange between intracranial compartments. In this emerging model, CSF has a direct correlation with the brain interstitial fluid (ISF), the blood circulation, and the lymphatic system. These new insights into the physiology and homeostasis of CSF, together with the new advances in neuroimaging, especially in MRI techniques, might have relevant implications for understanding the mechanisms at the base of brain pathologies.