[Odontoid bone. Apropos of a case].

Reporting a clinical observation, the authors emphasize upon the extreme scarceness of this variety of so called "congenital" pseudarthrosis of the odontoid process. The congenital origin, due to a lack of fusion, or the acquired one by avascular necrosis following a trauma is explained. The diagnosis may be clinical, consisting either on a vertebral syndrome occurring in childhood, or on a neurological syndrome in the adult age. It is mainly radiological : A scanner investigation is presented here. Owing to the potential neurological severity of the disease, the posterior fusion has to be recommanded.