Rheumatoid Arthritis- Craniovertebral Involvement

The spondylitis of RA is distinctive in that it has predilection for the cervical region. Osteoporosis, disc narrowing and end-plate irregularity are seen with only minimal reactive new bone formation in the upper cervical vertebrae in contrast to the osteoarthritis which involves lower cervical vertebrae.
Facet joint erosions may lead to subluxations at multiple levels in cervical spine giving STEP-LADDER appearance. Atlantoaxial joint subluxation is seen in 30% of cases especially in chronic disease due to involvement of transverse ligament with or without erosion of odontoid. (Separation between anterior border of odontoid and posterior surface of the anterior arch of atlas in flexion of more than 2.5 mm in adults or 4mm in children is considered diagnostic of AAD). The eroded odontoid at times may fracture.
In our case. T1 and T2 weighted images reveal pannus which is hypointense on T1 and T2 with erosion of odontoid peg. Altered signal intensity is also seen in cord at this level due to ischemia/oedema. Mild compression of thecal sac is also noted.

Reported by- Teleradiology Providers