Imaging of the Cervical Spine > Fractures > Atlanto-occipital Disassociation

Atlanto-occipital Disassociation

Description: Disruption of the atlanto-occipital junction involving the atlanto-occipital articulations.

Mechanism: Hyperflexion or hyperextension.

Radiographic features:

1. Malposition of occipital condyles in relation to the superior articulating facets of the atlas.
2. Increased ratio of Basion - spinolaminar line of C1 to Opisthion - posterior cortex of C1 anterior arch for incomplete anterior atlanto-occipital dislocation. (Refer to atlanto-occipital alignment for further explaination).
3. Cervicocranial prevertebral soft tissue swelling.

Stability: unstable

Here is an example of an anterior atlanto-occipital dislocation. Notice that the occipital condyles are anteriorly displaced in relation to the superior articulating facets of the atlas.

The first image on the bottom panel is a sagittal reconstruction of a CT scan for the same patient, which nicely delineates the displacement of the atlanto-occipital articulation. This displacement is also illustrated on the second image, which is a sagittal MRI scan through the same region. The last image is a sagittal MRI scan that demonstrates the cervicocranial prevertebral soft tissue swelling.