Mechanisms Involved in Cerebrospinal Fluid (CSF) Drainage and Interstitial Fluid (ISF)/CSF Exchange in the Central Nervous System (CNS)

For ages, the brain has been acknowledged as the most intricate and essential organ in the human body due to its immune-privileged nature, role in intelligence, and capacity for recognition, which sets us apart from other species. One of the most notable aspects of the brain is its unique lymphatic system (LS). Cerebrospinal fluid (CSF), which resembles an ultra-filtrate of plasma, is continually generated by the ependymal cells in the choroid plexus and flows steadily throughout the ventricular regions, making its removal from the brain essential. Moreover, a pathway exists that links the subarachnoid space (SAS) to the bony labyrinth of the inner ear through the perilymphatic canal, where the perilymph remains in continuity with the CSF. Despite significant progress in the field, studies on anatomical structures have yet to provide a precise explanation of the CSF drainage process. Various theories have been suggested regarding the drainage of CSF, including the roles of arachnoid villi and granulations, the glymphatic system, and the intramural periarterial drainage pathway; however, additional research is needed to fully understand these processes. This review consolidates the latest findings on CSF drainage from the brain, encompassing anatomical and cellular structures, the interactions between astrocytes, and other involved components.