Chiari Zero is when the cerebellum herniation of your chiari malformation is less than 5mm. There is still alot of disbute about chiari zero. Especially about if the herniation is large enough to cause your symptoms.
My opinion is that no matter what size the herniation it will still cause symptoms of Arnold Chiari Malformation. If there is something blocking the spinal cord fluids at all from flowing properly; this can casie problems
Please remember this is only my opinion.
Debra
