Arnold-Chiari malformation, sometimes referred to as the Chiari malformation, is an anomaly of the brain in which the brainstem is elongated, and pushed down through the opening of the base of the skull. The brainstem, cranial nerves and the lower portion of the cerebellum may be stretched or compressed. Therefore, any of the functions controlled by these areas may be affected.

In infants, the most common symptoms are stridor and swallowing difficulties. In older children, upper limb weakness and breathing difficulties may occur.

Arnold-Chiari Malformation occurs in almost all children born with both spina bifida and hydrocephalus.