Os odontoideum in achondroplasia: Rare Combination

This is a 45 yr old female with achondroplasia and 3D CT revealing os-odontoideum. This co-existence is relatively uncommon.

Os odontoideum-CT and MRI

Radiologic evaluation is utilized to confirm the diagnosis and estimate the degree of spinal instability. Os odontoideum appears as a round or oval ossicle with a smooth, uniform cortex separated from the base of the axis by a wide gap. The ossicle border does not directly match up with the axis body. The gap separating the os and the axis proper should lie above the level of the superior articular facets.