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Answer:
Pigmented villonodular synovitis.
Findings
- Plain film of the right hip demonstrates marked diffuse joint space narrowing with subchondral sclerosis and subchondral cyst formation.
- MRI of the right hip shows erosions about the right hip joint involving the femoral head and to a lesser degree the acetabulum.
- In the joint space, there is a mass characterized by intermediate signal on T1 weighted images and rather dark signal on the T2 weighted images. The mass extends posteriorly between the femoral neck and the ischial tuberosity.
- Gout
- Amyloid
- Synovial chondromatosis
- Hemophilic arthropathy
- Pigmented Villonodular Synovitis
- Pigmented villonodular synovitis (PVNS) is a benign proliferative disorder of uncertain etiology that affects synovial lined joints, bursae, and tendon sheaths.
- The disorder results in various degrees of villous and/or nodular changes in the affected structures.
- Two primary forms are described, including a diffuse form that affects the entire synovial lining of a joint, bursa, or tendon sheath, and a rare focal, or localized, form.
- The diffuse form typically involves the large joints, while the localized form typically occurs around the small joints of the hands and feet.
- Gross pathologic features include thickened synovium, with a combination of villous and nodular proliferation depending on the site of involvement.
- On microscopy, PVNS is characterized by the presence of hemosiderin-laden, multinucleated, giant cells. In addition, lipid-laden macrophages, fibroblasts, and other large, polyhedral-shaped, mononuclear cells are present; they have abundant cytoplasm and possess oval nuclei.
- PVNS typically invades local tissues; the invasion of the subchondral bone, with resultant cyst formation, is a characteristic finding.
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