Arnold Chiari Malformation, also known as Chiari type II malformation, is one of a group of brain malformations affecting the cerebellum. Named after Hans Chiari and Julius Arnold, the pathologists who first described the group of malformations. This condition is almosNormally the cerebellum and parts of the brain stem sit in an indented space at the lower rear of the skull, above the foramen magnum (a funnel-like opening to the canal). When part of the cerebellum is located below the foramen magnum, it is called a Chiari malformation. In Arnold Chiari Malformation, both cerebellar and brain stem tissue protrude into the foramen magnum and the cerebellar vermis (the nerve tissue that connects the two halves of the cerebellum) may be only partially complete or absent t always associated with myelomeningocele, the most serious form of spina bifida Dandy-Walker Syndrome (DWS) is a congenital (happening before birth) condition where the cerebellum does not develop normally. The cerebellum is an area at the back of the brain that controls movement and balance. With DWS, parts of the cerebellum may never develop or may be very small. Other parts of the cerebellum become filled with fluid or develop small masses of fluid (cysts). In most cases, a build-up of fluid inside the skull causes the head to get bigger than it should.