Pathological changes of the dura mater and chronic SDH (cSDHs). The number of vessels in the dural border cell (dbc) layer and outer membrane (OM) in the patient with cSDHs (Right side) was much higher than that in the dbc layer of the normal control (blue arrow). Newly formed vessels are composed of sinusoidal capillaries, which are thought to be a probable cause of repeat spontaneous bleeding because they are fragile and present in only the pathological dbc dural layer and OM of cSDHs. Such neovessels connect to surface middle meningeal arteries (MMAs) via penetrating arteries. Therefore, MMA embolization is a potentially effective way to block the blood supply to pathological membranes.