Sorry my private message box was full, it only allows me 60 messages in total, I can’t keep on top of it! You can post here though and I’ll try and answer.
Regarding a ‘retroflexed odontoid’ (uppermost peg-like bone which points backwards), mine is retroflexed but I do not qualify as Chiari 1 Malformation, which requires 5mm herniation of the cerebellar tonsils (lowest part of hindbrain), through the foramen magnum (hole in the bottom of the skull). I do have ‘low lying’ cerebellar tonsils, according to The Chiari Institute (NY), which abut the foramen magnum. When checking my symptoms years ago against those typical of Chiari, many were the same, I have to say.
Do you have a copy of your youngster’s MRI ?