Familial Dystopic Os Odontoideum

Abstract

In 1886, Giacomini1 described a rare lesion of the axis, os odontoideum, which was defined as an ossicle, consisting of smooth and separate caudal portions of the odontoid process. When it occurs, the caudal fragment of the odontoid may provide deficient stability for the atlantoaxial joint and lead to subsequent instability or dislocation and neurological deficits2-4. According to its location, os odontoideum has been classified into two anatomic types: orthotopic and dystopic4. Orthotopic os odontoideum consists of an ossicle that moves with the anterior arch of the atlas, while the dystopic type consists of an ossicle near the basion, or one that is fused with the clivus4. The etiology of os odontoideum has been debated. Some believe os odontoideum results from trauma of the odontoid3,5-9, the ligaments10, the epiphysis11, or the ossiculum terminale12. Others believe it has a congenital etiology3,13-18. A search of the English-language literature revealed four reports of familial os odontoideum19-22, which support a congenital etiology. Most of those patients with os odontoideum also had another congenital osseous deformity, such as Klippel-Feil syndrome, upper cervical hypoplasia, or opsismodysplasia. Proponents of an acquired etiology argue that, in such congenital deformities, the ligamentous hyperlaxity and incomplete ossification predispose to the development of traumatic os odontoideum23. Unlike the previous reports, we describe three generations of a single family, all of whom had an isolated and dystopic os odontoideum with no other osseous deformity in the craniocervical junction, suggesting a congenital etiology of the condition in this family. The family was informed that data on these patients would be submitted for publication, and they consented. The proband was a …