Total occipitalization of the atlas.

Occipitalization of the atlas is an important congenital malformation of the craniovertebral region because of the proximity to the spinomedullary region. In a sample of 109 human adult skulls of Asian origin examined for evidence of atlanto-occipital fusion, only one specimen exhibited this type of anomaly, in which the atlas was totally synostosed with the occipital bone with multiple bony defects. The embryological basis of this congenital abnormality is discussed.