What is an arnold chiari type 11?

Chiari type II (2)? Chiari malformations develop due to a decreased size in the back of the skull. Because there is not enough space for the brain to develop, a part of the brain called the cerebellar tonsils get pushed through through the hole where the spinal cord attaches to the brain. This results in increased pressure and development of "cysts" in the spinal cord. Chiari ii has additional brain&cord changes.