[Colliculus atlantis--a rarely observed anatomic structure--in a transoral roentgen image of the thoracic spine]

To study the time and mode of the development of the colliculus atlantis, the rate of its occurrence, the causes for its absence, and the radiological-clinical importance in the analysis of open-mouth-view radiographs.

Retrospective analysis of standardized radiographs of the cervical spine in more than 20,000 adults and 100 children. Study of 234 human skeletons of different ages and of 38 isolated adult atlases. Cadaveric dissection of 42 adults (age 48-87). Axial radiographs of isolated atlases and analysis of the bony structures of the colliculus atlantis.

The colliculus atlantis develops between age 10 and 13 years. It is always present after age 13 years. For the development of the colliculus atlantis a normal function of the craniocervical joints is necessary. In congenital dysmorphias of the craniocervical region with dysfunction of the craniocervical joints and in fractures of the dens axis before age 10 years with instable healing the colliculus atlantis is absent.

The colliculus atlantis is developed at age 13 years apart from some rare exceptions as mentioned. Changes of the site and the structure of the colliculus atlantis allow an early diagnosis of certain traumatically and inflammatory diseases of this region. Furthermore, it serves as an additional parameter in functional analysis of the craniocervical joints.