A 58-year-old mentally disabled man who slipped and fell in the shower. CT , computed tomography; Sag , sagittal.

A 56-year-old man who had been in a motor vehicle accident. CT , computed tomography; Sag , sagittal.

An 86-year-old woman presenting with neck pain. CT , computed tomography; Sag , sagittal.

A 45-year-old man with a history of a C3-C4 anterior cervical diskectomy and fusion presenting with neck pain after an assault. CT , computed tomography; Sag , sagittal.


  • Case A: A sharp, radiolucent dens fracture line without cortication is evident, separated by a very narrow fracture gap from the “matching” donor site. Prominent prevertebral swelling is seen.

  • Case B: A smooth, well-corticated, oval-shaped os odontoideum is seen at the expected site of the dens, with a wide gap separating it from the remainder of C2. Note the presence of a hypertrophic anterior arch of C1 and that the borders of the os do not directly match up with the remainder of C2. In addition, notice the presence of a narrow, interdigitating joint line between the os and the hypertrophied anterior arch of C1 (the “jigsaw sign”).

  • Case C: A sharp, radiolucent, narrow gap, dens fracture line is evident, with sclerosis along the fracture fragments and mild posterior displacement.

  • Case D: The patient had a prior C3-C4 anterior cervical diskectomy and fusion, as noted in the history. A small, smooth, well-corticated, oval-shaped os is seen along the superior aspect of the dens. The dens does not appear to be nearly as prominently truncated as in Case B.


Case A

Acute type II dens fracture

Case B

Os odontoideum (orthotopic)

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