CPPD Erosion of the Dens

Erosion of the dens with associated pseudotumour is classically associated with a pannus of rheumatoid arthritis, however many other causes are also possible. One of the more common other aetiologies, as in this case, is CPPD (calcium pyrophosphate deposition disorder).
As the pseudotumour enlarges it can directly compress the medulla, or more commonly lead to instability due to disruption of the transverse band of the cruciform ligament.
Also known as pseudogout, CPPD is a common condition, especially in the elderly, and is due to deposition of, as the name would suggest, calcium pyrophosphate in soft tissues and cartilage.
The three main manifestations of CPPD deposition are:
1. chondrocalcinosis
2. crystal induced synovitis (pseudogout syndrome)
3. pyrophosphate arthropathy
For a longer differential of dens erosion, and for more images of this case please visit University of Rochester Medical Imaging
Credit: Dr Frank Gaillard
http://www.radpod.org