Retro-odontoid pseudotumors, also known as periodontoid pseudotumors, are non-neoplastic soft tissue masses adjacent to the odontoid process (dens) of C2, which can cause cervicomedullary compression.
The prevalence of retro-odontoid soft tissue thickening, particularly with mineralization presumed to represent calcium pyrophosphate deposition, increases significantly with age .
These are often asymptomatic. Acute inflammation in these masses (as in crowned dens syndrome) can manifest as neck pain or headache. As a chronic process, mass effect on the cervical spine can manifest as myelopathy including sensory and motor deficits.
Pseudotumors can arise by various mechanisms and etiologies :
- atlantoaxial instability
- atlantoaxial hypermobility compensating for subaxial ankylosis
- deposition diseases
- calcium pyrophosphate dihydrate deposition disease (CPPD)
- hydroxyapatite deposition disease (HADD)
- amyloid arthropathy associated with hemodialysis
- dens fracture callus
- migrated disc herniation
Mineralization within the pseudotumor may be present in calcium pyrophosphate deposition disease (chondrocalcinosis, linear/arciform), hydroxyapatite deposition disease (cloudlike), gout (faintly), fracture callus, and ossification of posterior longitudinal ligament (by definition).
Bony erosion may be present in rheumatoid arthritis, calcium pyrophosphate deposition disease, gout, and pigmented villonodular synovitis.
Signal characteristics vary by etiology. In general, there are no reliable imaging features that distinguish rheumatoid arthritis-related pannus from non-rheumatoid retro-odontoid pseudotumor.
- T1: usually low
- T2: variable, often heterogeneous