Well there were 2 major findings on this one, but they are related. The one most people saw was the widened atlanto-dental space. Good job. But the one most people didn’t notice was the location of the dens. A little high? or perhaps inside the cranial vault?

I believe this case was all due to Rheumatoid Arthritis, but in the setting of trauma, CT and even MRI are probably good ideas unless you have prior exams.

Answer: Widened atlantodental space with basilar invagination

Reference: http://radiopaedia.org/articles/basilar-invagination

How about all the X-ray lines used to diagnosis it? http://radiopaedia.org/articles/radiographic-assessment-of-basilar-invagination