For example, as pinealomas, medulloblastomas, and ependymomas enlarge - the mass of the tumor can compress nearby ventricles blocking the flow of cerebrospinal fluid which causes swelling, called hydrocephalus.
This Arnold Chiari II malformation results in a variety of symptoms related to the cerebellum, and often resulting in hydrocephalus, an abnormal accumulation of cerebrospinal fluid in the brain.