Surgery is always a last resort for someone with a Chiari. It is a very serious surgery as Sky said, and because of the risks is generally used in patients with symptoms that become life threatening.

If there is a suspicion that you have this, an MRI is the only definitive test and you will need to have this test to confirm any diagnosis. If you do have to have one it should also have one with and w/out contrast. Just a few pointers from someone who knows

Good luck and keep us posted.