Congenital anomaly of combined atlas-odontoid process fusion and bipartite atlas.

Congenital fusion of the atlas with the odontoid process of the axis is a very rare condition caused by a segmental defect of the first cervical somite. Only 9 such cases have been reported in the literature to date. The bipartite atlas, another well-documented rare anomaly, has been observed in only 0.1% of the general population. We describe the first case of a 70-year-old male with both of these complex congenital anomalies.