A well corticated oval ossicle is seen above the body of C2, below the clivus, and behind the anterior arch of C1, corresponding to the os odontoideum.
A midline defect of the posterior arch of C1 (failure of midline fusion of the two hemiarches), type A according to the Currarino classification.
Note calcification within the anterior atlanto-axial ligament.
No cerebral or cervical spine traumatic lesion seen in this case.