Revisiting anterior atlantoaxial subluxation with overlooked information on MR images

Abstract

Background and purpose: The ADI is the imaging diagnostic clue to AAA subluxation of the cervical spine. Some MR imaging findings other than abnormal ADI relate to AAA subluxation. However, their relationship is not yet clarified. The present study elucidates the role of MR imaging by employing these previously overlooked findings.

Materials and methods: This study enrolled 40 patients with AAA subluxation and 20 non-AAA subluxation patients as controls. All MR imaging was performed with supine neutral positioning. The morphology of the dens, bilateral facet joints, and surrounding ligaments, as well as the alignment of the anterior atlantoaxial joint, the spinolaminar line, and the intramedullary signal intensity, were assessed. This investigation statistically analyzed the difference among these groups.

Results: Thirty-eight percent (15 of 40) of patients with AAA subluxation showed nAAA. There was no significant difference between the groups of AAA with normal and abnormal ADI except that more peridental pannus was seen in the latter group. More dens erosion (P = .022), tilting of anterior atlantoaxial joint (P = .022), peridental effusion (P < .001), lateral facet arthropathy (P < .001), abnormal spinolaminar line (P = .001), and focal myelopathy (P = .001) were observed in nAAA patients compared with the controls. The combination of peridental effusion, lateral facet arthropathy, abnormal intramedullary signals, and abnormal spinolaminar line showed a sensitivity of 100% and a specificity of 90% in diagnosing AAA subluxation.

Conclusions: MR imaging provides important biomechanical clues, other than ADI, that improve accuracy in diagnosing atlantoaxial instability.

Fig 1.

Midsagittal T2-weighted MR image in a 64-year-old woman with rheumatoid arthritis. The image shows that the posterior cortex of the anterior tubercle of C1 and the anterior cortex of the odontoid process are not parallel. Also note the abnormal spinolaminar line (arrow).

Fig 2.

Midsagittal T2-weighted MR image in a 72-year-old man with spondylosis. The image depicts focal high signal intensity at the cervical spinal cord (arrowhead). Note minimal fluid accumulation in the supradental region.

Fig 3.

Midsagittal T2-weighted MR image in a 69-year-old woman with rheumatoid arthritis. The image shows peridental fluid, pannus proliferation (arrow), and nonvisualization of the apical ligament. The atlantodental interval measured 7 mm on flexion radiograph (not shown).

Fig 4.

Normal apical ligament (arrow) and normal anterior atlantoaxial ligament (arrowhead) in the diagram (A) and the midsagittal T2-weighted MR image (B) in a 45-year-old woman with rheumatoid arthritis. Note the widened atlantodental interval (4 mm).

Fig 5.

Paramedian sagittal T1-weighted MR image in a 65-year-old woman with spondylosis. The image shows erosion of the lateral facet joint and bone marrow edema (white arrow).