Figure 1.

Schematic illustration of Waste Clearance (WC) in the brain. (A) Schematic model of cerebrospinal fluid (CSF) flow which is involved in brain WC, both within (B) and external to the brain parenchyma (C). Dotted arrows show the movement of CSF from the ventricular compartments to the subarachnoid space, entering the brain parenchyma via periarterial spaces, getting mixed with interstitial waste products as well as interstitial fluid (ISF), entering the perivenous space, and then draining via perineural spaces and lymphatics. The waste products also reach the vascular compartments directly via the blood-brain barrier (BBB) and indirectly via CSF exiting through the arachnoid villi/granulations. (Bi) A magnified schematic image of the glymphatic system and intramural periarterial drainage (IPAD) pathways involved in WC within the brain parenchyma. (Bii) A magnified schematic image of the vascular pathway via the BBB at the capillary level. (C) A schematic image of the CSF pathways involved in brain WC via the arachnoid villi (Ci), and lymphatic pathways [including the nasal lymphatics (Cii), and the meningeal lymphatics (Ciii)].