Atlanto-axial rotatory subluxation with 10 mm posterior displacement of C1 on C2 the left and widening of the left C1/2 facet joint. Remainder of the facet joints are enlocated and there is no other malalignment of the cervical spine. No acute fracture is identified.
Degenerative change at the atlantoaxial articulation with loss of joint space at the atlanto-dens articulation and soft tissue calcification; consideration should be given to depositional disease (e.g. CPPD) or an autoimmune process (less likely as erosions are not a predominant feature) causes.
Right posterior fossa craniectomy and plate reconstruction.
Conclusion:
Atlanto-axial subluxation. No acute fracture.