Craniovertebral (CV) junction anomaly is a congenital or acquired abnormality that involves the occipital bone of the cranium, the foramen magnum (where the brainstem transforms or continues as the spinal cord) and the first two cervical vertebrae. These disorders develop due to fusion of any of these structures, or due to underdevelopment or misalignment of the bony components. They can cause compression of the lower part of the brainstem, the cranial nerves, and the uppermost part of the spinal cord in the neck region. This will eventually lead to paralysis of the limbs, numbness, difficulty in walking and bladder incontinence.

The classification mainly includes Atlantoaxial dislocation/subluxation (AAD), Basilar invagination (BI), Platybasia, Klippel-Feil anomaly and Chiari malformations. Some of the acquired diseases like Rheumatoid arthritis, Paget disease and bone tumours like chordomas can lead to craniovertebral junction abnormalities. Injuries can lead to what is called as a traumatic Atlantoaxial or an Atlanto occipital dislocation.