Hydrocephalus is an abnormal accumulation of cerebrospinal fluid in the brain ventricles that causes them to expand. It can be caused by obstruction of CSF flow or improper absorption. Common signs include an enlarged head size, bulging fontanelles, downward eye deviation, and irritability. Diagnosis involves imaging tests and lumbar puncture. Treatment is typically with a shunt system to drain excess CSF out of the brain ventricles. Complications can include infection, shunt malfunction, and bleeding.