[Concepts of Cerebrospinal Fluid Management Based on a Paradigm Shift in CSF Dynamics:From the Third Circulation to...

Over the past century, cerebrospinal fluid (CSF) dynamics have largely been interpreted through the "third circulation theory," which posits that CSF is produced by the choroid plexus that flows from ventricles to the subarachnoid space and is absorbed mainly through arachnoid granulations. The concepts of the glymphatic system and meningeal lymphatic drainage have since driven a paradigm shift in this framework. In the glymphatic pathway, CSF enters periarterial spaces and, via aquaporin-4 channels on astrocytic endfeet, is exchanged with interstitial fluid to promote parenchymal waste clearance. Waste-laden fluid then exits along perivenous routes and is drained extracranially through meningeal lymphatics. Importantly, lymphatic pathways are not mechanically "plugged" by hemorrhagic CSF, and impaired clearance is more plausibly attributable to disrupted physiological pulsatility and sustained low-pressure conditions. Therefore, CSF management after subarachnoid hemorrhage should shift from prioritizing the removal of bloody CSF to restoring physiological CSF dynamics. Clinically, this supports minimizing drainage duration, pursuing early removal, and favoring intermittent over continuous drainage when feasible. Patients presenting with acute hydrocephalus constitute a distinct subgroup in whom ventricular drainage is often unavoidable, and subsequent shunt dependency is more likely.