What is the role of MRI in the workup of spinal involvement in rheumatoid arthritis (RA)?

Updated: Nov 01, 2018
  • Author: Michele Calleja, MD, FRCR, MRCP; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Answer

The major role for CT and MRI is in the preoperative assessment of the 2 main indications for surgical intervention: neurologic deficit and severe pain. [14, 15] The subluxations that are of a degree likely to result in paralysis need to be identified, as better outcomes have been reported with earlier interventions. The effect of pannus and intracanal granulations on the cord cannot be accurately assessed on plain images, despite the fact that a posterior atlantodental interval (PADI) of less than 14 mm is a sensitive indicator of paralysis risk. [3, 9, 16]

(See the images below.)

T1-weighted sagittal MRI of the cervical spine sho T1-weighted sagittal MRI of the cervical spine shows basilar invagination with cranial migration of an eroded odontoid peg. There is minimal pannus. The tip of the peg indents the medulla, and there is narrowing of the foramen magnum due to the presence of the peg. Inflammatory fusion of several cervical vertebral bodies is shown.
Sagittal T2-weighted MRI of the cervical spine in Sagittal T2-weighted MRI of the cervical spine in the same case as in Image above. The compromised foramen magnum is easily appreciated, and there is increased signal intensity within the upper cord; this is consistent with compressive myelomalacia. Further narrowing of the canal is seen at multiple levels.

Although CT scanning can document bone damage and alignment abnormalities, especially with more detailed multiplanar reconstruction, MRI has become the preferred modality for evaluation of the spinal cord and neural elements. [5] It demonstrates the presence and effect of pannus on the spinal cord and is useful in assessing its resolution following posterior fusion and stabilization. On MRI, the direct relationships of the odontoid to the medulla and brainstem can be documented. Spinal cord signal can be assessed; edematous changes in the cord are associated with a poor clinical status, as well as a poor prognosis and a poor postoperative outcome. [6]

The major indications for MRI in RA are abnormal measurements on plain radiographs, [17] unremitting suboccipital/cervical pain, progressive/severe subluxations, symptoms of cord/brainstem compression, and vertebral artery compression.

Dynamic MRI has been used with the patient in a flexed or extended position and in the traditional neutral position. Roca et al suggested that functional (flexed position) MRIs be obtained in patients with RA in whom cervical subluxation is suspected when routine MRI findings in the neutral position are normal. [18] Others recommend functional MRI as a preoperative examination. [19]

Pathologic series have suggested that cord atrophy in rheumatoid cervical myelopathy results from repeated traction injury as a result of compression, stretch, and movement as opposed to an inflammatory process per se. This is unsurprising considering that the atlantoaxial joint is the most mobile segment of the cervical spine.

In a study looking at the features of rheumatoid cervical myelopathy on MRI that were associated with subsequent deterioration, it was determined that in cases in which axial compression or impingement was identified on MRI, 60% of patients experienced deterioration resulting in death or surgical intervention over a median period of 12 months.

When functional imaging is performed, patient monitoring is advised, and rapid sequences are desirable because patients may find the flexed position uncomfortable. Some authors suggest that functional MRI is unnecessary and even contraindicated in patients in whom medullary or spinal cord compression is discovered on studies made in the neutral position.


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