As said, surgery is not a cure for Chiari because it still causes pain and a lot of treatment. Estrogen is a hormone in girls I believe. It triggers bone growth and density. What if they were able to focus it on the part of the skull that is undeveloped or not big enough. Like replace the part that's pressing against the spin with like some type cartilage thing, behind the skull, pressing the cartilage like thing into what shape the back is supposed to form, and focus the estrogen on that certain area, but just not too much and when the skull is fit into the right place, remove the cartilage like thing and pull down the bottom lobe of the brain to where it is supposed to be!