Hi Shannon,

My suggestion would be to contact TCI - The Chiari Institute
they have the best Docs and a wonderful staff.

Their website contains a great deal of information and basilar invagination is listed under related conditions.
"What other conditions are related to Chiari malformation?
Other Chiari-related disorders treated at the Chiari Institute include basilar invagination (protrusion of the upper end of the spine into the skull); craniospinal instability; intracranial and intraspinal cysts; tumors of the cerebellum, brain stem and spinal cord; spina bifida; spinal cord tethering; hydrocephalus (a buildup of CSF in the cavities of the brain); and pseudotumor cerebri (chronically raised CSF pressure)."

Hope this is helpful and you find the answers you are seeking. It's always a difficult time when you are informed of health challenges. Try and take it one step at a time with lots of deep breaths!!
Blessings!