persistent ossiculum terminale
The ossiculum terminale appears as a secondary ossification center of the dens between 3-6 years and normally fuses by 12 years. Failure of fusion results in a persistent ossiculum terminale (also called Bergmann's ossicle or ossiculum terminale of Bergmann) and is considered a normal anatomical variant of the axis.
It lies above the alar ligament and is therefore considered to be stable and it very rarely causes symptoms.
- small, well-corticated ossicle at the tip of the dens
- usually in the midline
- dens is typically normal in height