November 12, 2009

Os Terminale - Os Odontoideum Complex (2)

Sagittal reformatted CT image shows an os terminale, sitting on top of the normal-sized dens.

Os Terminale
  • Derived from the 4th occipital sclerotome but does not undergo fusion with the dens
  • The dens is normal in size and shape
  • If it enlarges, coupled with dens hypoplasia -- it is called os odontoideum
  • Usually single, smooth
  • Sometimes can show bony fragmentation mimicking a comminuted fracture (but one should be aware that an extensively comminuted fracture at the tip of the dens is extremely rare or nonexistent)
Reference:
Swischuk L. Imaging of the cervical spine in children, 2004.

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