Describe the abnormality
Bilateral sacroiliac joint space narrowing, subchondral erosions, subchondral sclerosis, and subchondral fatty marrow infiltration.
What is the differential diagnosis?
Bilateral symmetrical:
Ankylosing spondylitis
Inflammatory bowel disease.
Bilateral asymmetrical:
Psoriasis
Reactive arthritis (Reiter syndrome)
What is the most likely diagnosis?
Ankylosing spondylitis
What are the markers of active inflammation?
Erosions with high signal intensity on STIR or T2- weighted images, subchondral edema, and enhancement within or adjacent to the sacroiliac joint.
What are the markers of chronic disease?
Low signal intensity on T1- and T2- weighted images, subchondral sclerosis, narrowing of the joint spaces, bone bridging, and ankylosis.
