basilar invagination
英[ˈbæsilə inˌvædʒiˈneiʃən]美[ˈbæsəlɚ ɪnˌvædʒəˈneʃən]
Basilar invagination occurs when the top of the C2 vertebrae migrates upward. It can cause the opening in the skull where the spinal cord passes through to the brain (the foramen magnum) to narrow.