What is the difference between arnold chiari malformation and chiari malformation?

Same: No difference, in short form people call as chiari malformation.

Clinical findings: Chiari described different forms of malformation of the cerebellum. His type 2 was found associated with spina bifida and other defects in formation of the brain, brainstem, and spinal cord. This was elaborated by arnold. Therefore, chiari 2 has now been called the arnold chiari malformation.

Big difference: Arnold chiari is a chiari ii malformation which is usually associated with spina bifida and involves herniation of the cerebellar vermis. On the other hand, what typically is diagnosed in young adults is a chiari i malformation which involves herniation of the cerebellar tonsil and is not associated with a neural tube defect.