Os odontoideum is a distinct oval and/or circular bone fragment which is segregated from the hypoplastic odontoid process. This is the most frequently detected anomaly of the odontoid process that may cause atlanto-axial instability and myelopathy. This anomaly can mimic Type I and II odontoid fractures. Accurate diagnosis is mandatory to prevent treatment failures. In this study, we present a 22 year- old female patient with severe neck pain. Diagnosis of os odontoideum was established, and the diagnosis of acute odontoid fracture was discarded in this 22 year-old female patient with radiologic findings such as characteristic cortex with smooth contours, no history of recent trauma, sclerosis and hypertrophy of the anterior tubercle of the atlas. Radiological methods used in the diagnosis and differential diagnosis of this case were discussed in detail.

Keywords: Os odontoideum, differential diagnosis, radiology, dynamic CT