Familial Os Odontoideum: Proatlas Segmentation Abnormality

Os odontoideum is a smooth, independent ossicle separated from a hypoplastic odontoid process located cranially in the expected position of the odontoid tip. The pathogenesis of os odontoideum remains controversial, and several etiological theories have been suggested for congenital, developmental, and traumatic origins.

We have reported symptomatic familial cases of dystopic os odontoideum in 2 elderly sisters who denied any traumatic history of the head and neck. Both patients were treated surgically, with successful outcomes achieved.

When examining the etiology of os odontoideum, checking for the existence of a traumatic history is important. However, a more important matter is to consider morphological segmentation abnormalities of the proatlas. Segmentation abnormalities of the proatlas could be closely connected to the development of familial os odontoideum.