Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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November 3, 2014
Down Syndrome with Atlantoaxial Instability and Persistent Ossiculum Terminale
- Patients with Down syndrome are at high risk for atlantoaxial instability (AAI). Hypoplastic dens and persistent ossiculum terminale are often associated.
- The classification of odontoid process abnormalities is complicated and controversial. According to the theory of Greenberg, based on the concept of anomalous segmentation, failure of the odontoid tip to fuse with the odontoid proper beyond the age of 12 is termed persistent ossiculum terminale.
- Key Diagnostic Features:
- Plain films and CT (better demonstrated on plain films) will demonstrate AAI (> 5 mm in pediatric population and > 3 mm in adults).
- Hypoplastic dens and persistent ossiculum terminale are associated findings.
- Signal abnormality within the cord, suggestive of edema versus myelomalacia, can be seen.
- DDx:
- Fracture (type I or II dens fracture)
- Rx: Surgical internal fixation
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