Arachnoid granulations, also called arachnoid villi, are tiny outpouchings of the arachnoid membrane that protrude into the dural venous sinuses. Their primary function is to reabsorb cerebrospinal fluid from the subarachnoid space back into the venous blood. They can sometimes be seen on ultrasound as small, round structures within or adjacent to the venous sinuses of the brain. While they are a normal anatomical finding, they can occasionally be mistaken for blood clots or small tumors, so sonographers should be aware of their existence and typical appearance.
Sonography Term