What is the success rate of cranial fusion surgery on an adult chiari patient?

Why surgery? Chiari is a congenital finding of low position of the cerebellar tonsils. This is usually incidental and not clinically significant. It can be seen on MRI done for headaches, but is not the cause of headaches. Surgery should be avoided unless there is definite indication. Common time for problems is during rapid growth before puberty - not as adult.