Odontoid process agenesis

Last revised by Dr Henry Knipe on 15 Mar 2021

Odontoid process agenesis is rare, occuring due to a lack of failure of ossification of the odontoid process. It is seen in patients with spondyloepiphyseal and spondylometaphyseal dysplasia 1,2.

On plain film, odontoid process agenesis appears small, as a slight depression on the superior articular facet on open mouth view or hypo genesis of basal segment of odontoid with floating apical process. Both of these conditions are associated with atlantoaxial instability.

On dynamic CT scan both flexion and extension views should be performed, to identify posterior subluxation.

Atlantoaxial instability will lead to vascular compression and stroke because of ischemia 2,4. Treatment options include a surgical fusion of C1 and C2.

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