Atlanto-occipital fusion

Atlanto-occipital dislocation, orthopedic decapitation, or internal decapitation describes ligamentous separation of the spinal column from the skull base. It is possible for a human to survive such an injury; however, only 30% of cases do not result in immediate death. [Source: Wikipedia ]

Atlantooccipital fusion
Occipitalization of atlas
May Cause
Atlantoaxial instability
Congenital craniovertebral junction abnormality
May Be Caused by
Klippel-Feil syndrome