What abnormalities are visible on these films?
Fracture of the posterior arch of C1 along with widening of the atlantodens interval (seen on lateral). On AP odontoid (peg) view, the lateral masses of C1 are displaced laterally.
What is this fracture called?
Jefferson's fracture (C1 burst fracture)
PEG view demonstrates lateral displacement of the lateral masses of C1 with respect to C2 meaning the bony ring of C1 must be disrupted (normally the lateral bony margins of C1 should not overhang C2). Lateral views of the cervical spine (with a hard collar applied) demonstrate widening of the atlantodens interval and a lucency (fracture) can also be seen traversing the posterior arch.