I would also like to point out that, according to the Chiari Institute in New York (check out their website for some excellent videos and explanations) even though this is the usual MRI shot for determining Chiari (or any degree of cerebellar ectopia) it’s not always a true reflection of what’s going on.
Also, some people show a normal brain when laid down but the picture changes when you’re in an upright position, hence the benefit from having an upright MRI.
Regards
Barbara
(UK)