Atlas assimilation: a case report

Congenital and acquired bony abnormalities of the cranio-vertebral junction may result in compression and distortion of the neural structures, vertebro-basilar vascular system, and cerebrospinal fluid channels. Ninety-eight human skulls of both sexes were examined for occipitalization of atlas. Two crania showed various degrees of assimilation of the atlas to the basicranium. One of the skulls showed complete fusion of the atlas with the occipital bone. Whereas, in the other skull atlas was partially fused to the occipital bone. Even though assimilation of the atlas is the most common anomaly found in cranio-cervical junction, head and neck surgeons should be aware that such an anomaly may exist without any typical symptomatic presentation, and thus, serious consequences of upper cervical spinal manipulative therapy may arise when a complete and adequate clinical assessment is missed.