Arachnoid villi

The arachnoid villi also known as arachnoid granulations are protrusions of the arachnoid membrane into the dura mater. The prtrusions lie next to the venous sinuses of the dura, and allow for the passage of cerebrospinal fluid out of the subarachnoid space directly into the venous blood. They are a major site of CSF reabsorption when the intracranial pressure is high. A major site of arachnoid villi is the superior sagittal sinus.