This 53-year-old male presents with popping and pain on top of the left shoulder with decreased range of motion. You are shown five images: a coronal T1 (image 1), coronal T2 (images 2, 4), and a sagittal T2 turbo spin echo SPAIR or fat-suppression sequence (images 3, 5). Images 4 and 5 are duplicates of images 2 and 3, but with arrows added for key findings. See what you can figure out just by looking at the first three images.
Q1 – What is the most likely diagnosis?
Q2 – What is your differential diagnosis?
Q3 – What is the important difference between the primary and secondary forms of this disorder?
A1 – Primary synovial chondromatosis.
A2 – Differential diagnosis includes secondary synovial chondromatosis as a manifestation of osteoarthritis; donated chondral bodies from osteochondral defects; osseous bodies; and synovial hyperplasia.
Secondary synovial chondromatosis is usually associated with osteoarthritis and you would have been shown an arthritic joint. Chondral bodies are usually not this organized in their shape and size, namely elliptical and smooth. Further, you would have been shown the osteochondral donor site. Osseous bodies would be marrow containing or brighter on T1 and more hypointense on T2. Synovial hyperplasia is not quite so organized and elliptical in shape. The fronds of synovial hyperplasia are smaller. Furthermore, this is a 53-year-old male and synovial hyperplasias are associated with rheumatoid arthritis and seen in women. You would have also been shown other signs of rheumatoid arthritis.
Other unusual intraarticular hypointensities include amyloid (rare) which is not quite so organized in shape; gouty tophi also not so organized in shape; and localized PVNS (more hypointense on T2 and more hyperintense on T1).
A3 – It is important to distinguish primary from secondary synovial chondromatosis as the primary form can be associated with malignant degeneration while the secondary form has no association with increased incidence of malignancy.
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