Cerebrospinal fluid (CSF) is produced at a constant rate in the choroid plexuses of the lateral and third ventricles, and it predominately drains through the Sylvius aqueduct to the fourth ventricle. If the Sylvius aqueduct becomes obstructed, such as caused by a growing tumor adjacent to it, CSF accumulates in the ventricles and the ventricles expand significantly, leading to a medical condition known as noncommunicating, hydrocephalus.