a series of extensions found in the middle layer of the meninges (arachnoid mater) and throughout the outer layer (dura mater) that actually permit cerebrospinal fluid to drain into the bloodstream.

Protrusions of the arachnoid membrane of the brain. The arachnoid villi (or granulations) are very similar to a one-way valve, as they allow the CSF to drain from the subarachnoid space into the superior sagittal sinus, where it can be reabsorbed into the blood system.

Tufted prolongations of pia-arachnoid, composed of numerous arachnoid villi that penetrate dural venous sinuses and effect transfer of cerebrospinal fluid to the venous system. at advanced age these are more numerous and tend to calcify. Synonyms: granulationes arachnoideales, arachnoidal granulations, pacchionian bodies, pacchionian corpuscles, pa [..]