Hi and welcome to the Chiari forum.
Craniometaphysical Dysplasia for those that do not know is a thickening of the bone.....and I could see this being an issue to cause flow of CSF to be obstructed....but I am not aware of anyone else so far on this forum with this condition as well as Chiari.....
His symptoms do seem to be what most of us deal with....so he is not alone on that....as for the bone being thicker, this may take longer for the surgeon to do this procedure, but as long as he has confidence in his surgeon then he should be fine....
This surgery typically can take 3 to 4 hrs,....mine was 7.5.....we are all different,.....and that is ok......
Best advice....expect the unexpected and let his body take all the time it needs to recover....no one can give a time line on how long b4 he does this or that...but it is best not to try for a few months as we can feel great and think we can do things....but doing too much too soon can cause set backs,,.....slow and steady is best.
Please add your DS's name to our surgery date thread so a Prayer Thread can be posted for him.
http://www.medhelp.org/posts/Chiari-Malformation/-List-ur-Surgery-Dates-2014/show/2049539