Morphology of the Arachnoid Villi and Granulations

The morphology of the arachnoid villi and granulations were studied in recently sacrificed dogs and sheep. Alatex-like material was perfused through the subarachnoid space under near-normal pressure conditions filling open pathways and spaces in the villi. This technique demonstrated that passage of cerebrospinal fluid through the arachnoid villi is at least in part a passive process through open communications. Also, arachnoid villi and granulations show a pressure-dependent "valvular" mechanism which aids in transference of cerebrospinal fluid from the subarachnoid space to the venous sinus and prevents reflux of blood into the subarachnoid space.