Chiari Decompression is a surgery done to allow more room for the cerebellum, the part of the brain that is just above the nape of the neck. The two halves of the cerebellum generally lie entirely within the skull. In a Chiari Malformation, however, the lowermost part of the cerebellum, called the tonsils, herniate through the opening at the base of the skull. This can result in pain and other neurologic disturbances. A Chiari Decompression relieves pressure on the brain and allows the cerebrospinal fluid to resume normal circulation.