Bipartite atlas with os odontoideum: case report.

STUDY DESIGN: A case report of bipartite atlas associated with os odontoideum and review of the pertinent literature are presented.

OBJECTIVE: To illustrate an unusual association of bipartite atlas and os odontoideum and explain the embryological basis.

SUMMARY OF BACKGROUND DATA: To the authors' knowledge, only one case of bipartite atlas with os odontoideum had been reported previously. Most of the previously reported cases of bipartite atlas are asymptomatic.

METHODS: A 16-year-old boy presented with a 2-month history of weakness and numbness of all four limbs after sustaining a minor head trauma. Radiographs of cervical spine revealed aplasia of anterior arch of atlas, ventral displacement of C1 over C2 on flexion, which reduced on extension. CT scan showed anterior arch aplasia, posterior arch midline defect, and os odontoideum, which had a small projection on the anterior surface at the level of anterior arch. MRI demonstrated increased cord signal at C1-C2 levels on T2-weighted image. Transoral odontoidectomy and posterior fixation of occiput with C2-C3 spinous processes was performed.

RESULTS: The patient had significant improvement over next 3 months.

CONCLUSIONS: We described a rare association of an anterior arch aplasia, posterior arch defect and os odontoideum. The natural history of patients with os odontoideum suggests that these people have a potentially precarious existence.