Presentation
Right knee pain. No trauma.
Patient Data
Diffuse irregular thickening and proliferation of the synovial lining of anterior and posterior recesses of knee joint, forming nodular and villous projections associated with moderate joint effusion. These projections display low T1, intermediate T2, and bright STIR signal. The synovial membrane, as well as some of the nodular projections, exhibits low T2 signal intensity, suggesting possible hemosiderin deposition. Some of the synovial masses imprint the surface of the adjacent bone, causing erosion best seen at the patellar eminence.
Baker cyst with thickened wall, medial and lateral gastrocnemius bursae are seen as well.
The posterior horn of the medial meniscus shows faint high MR signal not interrupting its articular surfaces (grade I degeneration).
Mild increased MR signal and blurred outline of the anterior cruciate ligament, yet no evidence of fiber disruption (ACL sprain).
Patchy ill-defined areas of altered marrow signal are seen at the distal end of the femur as well as the proximal end of the tibia, sparing the epiphyses, likely representing bone marrow reconversion.
Case Discussion
The above-described features are suggestive of the diffuse form of pigmented villonodular synovitis.
Pigmented villonodular synovitis (PVNS) is a rare benign proliferative condition affecting synovial membranes of joints, bursae or tendons, possibly resulting from neoplastic synovial proliferation with villous and nodular projections and hemosiderin deposition. PVNS is most commonly monoarticular (the knee followed by the hip joints are the most common sites) but occasionally can be oligoarticular. The histology of PVNS can look similar to some aggressive neoplasms (e.g., synovial sarcoma) and imaging, therefore, has a crucial role in guiding the pathologist.
PVNS has two forms:
- diffuse form characterized by joint effusion and extrinsic bony erosions, but the joint space is unaffected.
- localized forms characterized by only a soft-tissue mass.
Special thanks to Dr. Amr Gamil, MD.
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