Arnold-Chiari malformation references on wikipedia
Arnold-Chiari_malformation Arnold-Chiari malformation is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils and the medulla through the foramen magnum, sometimes causing hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow . The cerebrospinal fluid outflow being caused by phase difference in outflow and influx of blood in the vasculature of the brain.