Canine Hydrocephalus (or "water on the brain") is caused when the cerebrospinal fluid (CSF) in the brain accumulates either because of a congenital defect, obstruction or the result of perinatal trauma, placing pressure on the brain. This usually occurs in young dogs under the age of 18 months and older dogs that are over 6 years of age. If Hydrocephalus is left untreated could be fatal. Treatment consists of medical treatment and surgery where either the obstruction is removed or a shunt is inserted. The Chihuahua, Maltese, Pekingese, Pomeranian, and Yorkshire Terrier are particularly at risk for the disease, but any breed has a chance of developing it.