Typical MR changes in ankylosing spondylitis depend on the disease stage.
Early stage: Signs of disease activity in the form of oedema and/or contrast enhancement in the joint space and surrounding bone. The changes are often bilateral, but may be unilateral and vary from side to side over time. There are often accompanying chronic changes in the form of erosion, joint space alteration and fatty deposition in bone marrow at the first examination.
Middle stage: Is often dominated by chronic changes (erosion, joint space alteration in the form of narrowing or widening and fatty deposition in the bone marrow). During active stages the chronic changes are mixed with signs of activity (oedema and/or contrast enhancement), which can vary from side to side.
Late stage: Increasing joint destruction with partial or complete fusion (ankylosis) of the joints, which can appear as "ghost joints" (ankylosis with visible joint contours).