Atlantooccipital and Atlantoaxial Separation

Sagittal T2 magnetic resonance imaging shows the anterior atlantooccipital ligament ( white arrow ), anterior arch of C1 ( black arrow ), dens ( magenta arrow ), apical ligament ( blue arrow ), tectorial membrane ( green arrow ), basion ( yellow arrow ), and opisthion ( red arrow ).

Flexion and extension lateral radiographs show normal alignment on the extension view but significant anterior translation of the atlas with respect to the dens on the flexion view.

Sagittal computed tomography image shows superior subluxation of the dens through the foramen magnum. Erosive changes also are affecting the dens.