Thinking beyond pannus: a review of retro-odontoid pseudotumor due to rheumatoid and non-rheumatoid etiologies

Skeletal Radiol. 2019 Oct;48(10):1511-1523. doi: 10.1007/s00256-019-03187-z. Epub 2019 Mar 13.


Retro-odontoid pseudotumor, or mass-like retro-odontoid soft tissue thickening, is an uncommon but important imaging finding that may be associated with rheumatoid arthritis, crystal deposition diseases, as well as non-inflammatory conditions such as cervical degenerative changes and mechanical alterations. Retro-odontoid pseudotumor is commonly associated with atlantoaxial microinstability or subluxation. MRI and CT have an important role in the detection and diagnosis of retro-odontoid pseudotumor. However, due to a wide range of imaging characteristics and ambiguous etiology, it is a frequently misunderstood entity. The purpose of this article is to review relevant anatomy of the craniocervical junction; describe various imaging appearances, pathophysiology and histology in both rheumatoid and non-rheumatoid etiologies; and discuss differential diagnosis of retro-odontoid pseudotumor in order to help guide clinical management.

Keywords: Atlantoaxial; Cervical spine; Odontoid; Pannus; Retro-odontoid pseudotumor; Rheumatoid arthritis.

Publication types

  • Review

MeSH terms

  • Arthritis, Rheumatoid / complications*
  • Atlanto-Axial Joint / diagnostic imaging*
  • Humans
  • Joint Dislocations / diagnostic imaging*
  • Joint Dislocations / etiology
  • Magnetic Resonance Imaging / methods*
  • Odontoid Process / diagnostic imaging*
  • Spinal Diseases / diagnostic imaging*
  • Spinal Diseases / etiology
  • Tomography, X-Ray Computed / methods*