Retro-odontoid pseudotumors or pannus are deposits – mostly in the area behind the dens – resulting from instability. It is an indirect sign of instability.
There are different biochemical structures which form a pannus:
– Micro- hemorrhages
– Deposits of calcium pyrophosphate dihydrate (crowned dens syndrome)
Depending on how the pannus is built it is shown at different sequences in the MRI.