Arachnoid granulations (English)

The brain is surrounded by three layers of meninges known as the dura, arachnoid, and pia mater. These layers delimitate three clinically important spaces: the epidural (or extradural), subdural, and subarachnoid spaces. Arachnoid granulations (Pacchionian granulations) are evaginations of arachnoid mater that pierce the dura mater and protrude into the lumen of the superior sagittal sinus and adjacent lateral lacunae. The core of each arachnoid granulation contains arachnoid trabeculae and is continuous with the subarachnoid space, therefore containing cerebrospinal fluid. The surface of each arachnoid granulation contains smaller outpouchings called arachnoid villi that increase its absorption surface. The main function of these granulations is to drain cerebrospinal fluid from the subarachnoid space into venous circulation, thus maintaining appropriate CSF pressure.