Rheumatoid arthritis of axial skeleton

  

Definition

• Chronic progressive systemic inflammatory disease in which joints are primary target

 

IMAGING

• Purely erosive disease, most frequently involving C1-C2

 

• Radiographic findings

○ Dens erosions

○ Atlantoaxial subluxation

○ Atlantoaxial impaction: May be unilateral or bilateral

  If unilateral, collapse results in torticollis

○ Subaxial subluxation

○ Sternoclavicular joints involved in 30% of patients with RA but difficult to visualize on radiograph

○ Osteoporosis

 

• Radiographs must include lateral flexion-extension

 

• CT: Additive to radiographs

○ Extent of erosive disease more apparent

○ Atlantoaxial (AA) impaction well shown

 

• MR: Additive to radiographs

○ Pannus, usually around odontoid, distinctly seen

○ Cord compression and damage directly visualized

 

• Best imaging tool

○ Radiographs, with lateral flexion-extension

 

○ CT: Additive to radiographs

– Erosion extent better visualized

– AA impaction well shown

 

○ MR: Additive to radiographs

– Pannus distinctly seen, usually around odontoid

– Cord compression and damage directly visualized

 

CLINICAL ISSUES

• Patients with axial disease rarely show associated symptoms until very late

○ Cord symptoms with atlantoaxial impaction

○ Cord symptoms with > 9 mm atlantoaxial subluxation

○ Unilateral C1-C2 facet disease → painful torticollis

• Patients with axial disease virtually always have significant peripheral disease (hands/feet) as well

 

DIAGNOSTIC CHECKLIST

• Watch location of anterior arch of atlas relative to odontoid to evaluate for atlantoaxial impaction

○ Anterior arch should align with upper portion of dens

• Remember AA subluxation may be underestimated on neutral lateral radiograph and CT

 

 Graphic in axial and sagittal planes through the atlantoaxial level of the cervical spine demonstrates the inflammatory pannus surrounding the odontoid process that frequently occurs in patients with rheumatoid arthritis (RA). Note the erosion of the odontoid, as well as focal compression of the spinal cord.

 

 

Sagittal T2WI MR shows extensive erosive changes of the odontoid process  as well as a large amount of pannus with effacement of the thecal sac and posterior displacement of cord.

 

Lateral x-ray shows severe (> 9 mm) atlantoaxial (AA) subluxation and impaction. Note the disruption of the spinolaminar line at C1- C2. Many of the facets are eroded, and abnormal motion of osteoporotic bone results in endplate destruction and subluxation at the C5-C6 level .

 

 

Sagittal CT in the same patient emphasizes the severe odontoid erosion and AA subluxation with impaction. There is no soft tissue swelling at C5-C6 indicating that the disc space loss is mechanical rather than infectious.

 

Lateral radiograph shows AA subluxation. Even more importantly, the anterior arch of the atlas is in a low position relative to the odontoid. This indicates AA impaction. The actual impaction is difficult to visualize radiographically because of superimposed mastoid processes.

 

 

Lateral radiograph of the same patient 1 year later shows the anterior arch of the atlas  located at the level of the body of the odontoid . The AA impaction is severe.

 

 

Sagittal CT shows a typical pattern of cranial settling in RA due to AA impaction. There is upward translocation of the dens with respect to the foramen magnum ; Wackenheim clival line is abnormal. Dens erosion and AA subluxation are noted as well.

 

 

Sagittal STIR MR of the same patient shows the impacted dens position and narrowing of the subarachnoid space at the foramen magnum with cord compression between the odontoid and opisthion .

 

 

Sagittal NECT shows severe erosive changes of C1 and odontoid process . The location of the remnant of anterior arch of C1 opposite the body of C2 indicates AA impaction.

 

 

Coronal NECT shows the impacted tip of the eroded odontoid . It also demonstrates the erosions and collapse of the lateral masses (facets) at C1-C2 . Compare this to the facets of the subaxial spine, which are normal. It is the collapse of the lateral masses that results in AA impaction.

 

 

Sagittal bone CT in a patient with RA shows erosions at multiple levels in the cervical spine, causing instability at occiput-C1, AA subluxation , AA impaction (cranial settling) , as well as endplate erosions and uncovertebral erosions at lower levels . Such diffuse involvement is common.

 

 

AP radiograph in a patient with RA shows angulation of the mandible . The cervical spine is straight; this mandibular tilt should suggest unilateral atlantoaxial impaction.

 

 

Open mouth odontoid radiograph in an RA patient with acute torticollis shows a normal right C1-C2 facet but eroded left C1-C2 facet. This discrepancy may result in unilateral collapse of this joint and associated painful torticollis.

 

 

Coronal bone CT of the same patient confirms the erosions and collapse of the left C1-C2 facet compared with the normal right C1-C2 facet. Note that the occiput-C1 facets  are normal as well.

 

 

 Sagittal bone CT in this same RA patient shows the erosions and collapse of the left C1-C2 facet .

 

 

 The normal right C1-C2 facet joint in this same patient is shown for comparison. Facet joints are at risk for erosive disease at any location of the spine. However, C1-C2 facets seem particularly at risk. If both C1-C2 facets erode and  collapse, the patient may develop AA impaction. With unilateral collapse, the patient develops a painful torticollis.

 

Lateral radiograph in an RA patient with normal AA structures shows erosive change of multiple facet joints This has not yet resulted in abnormal alignment or endplate destruction.

 

 

Lateral radiograph in a patient with RA shows severe erosive disease, resulting in atlantoaxial subluxation, facet erosions, and presumed ligamentous disruption. The combination leads to malalignment and subsequent endplate mechanical erosions and disc destruction.

 

 

 

 Sagittal NECT shows C1- C2 impaction . The odontoid process is eroded . The subaxial spine shows marked diffuse disc and endplate degeneration due to a combination of ligamentous disruption and facet/uncovertebral joint erosions.

 

 

 Sagittal STIR MR shows pannus formation causing severe cord compression. C1-C2 subluxation and impaction are prominent. Multilevel subluxations of the subaxial cervical spine reflect facet and uncovertebral involvement.

 

 

Sagittal CT shows RA C1-C2 impaction. Note the fusion at several vertebral bodies . Fusion in RA is uncommon but may occur at the site of these mechanical erosions and disc degeneration.

 

 

 

Lateral x-ray shows mild atlantoaxial subluxation and severe atlantoaxial impaction . Note also the eroded facets at multiple levels as well as the thinned spinous processes , typical of RA. The patient has mild stair-step subluxations of the vertebral bodies secondary to a combination of abnormal motion and osteoporosis.