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villonodular tenosynovitis

Saturday 19 December 2020

Tenosynovial giant cell tumour, diffuse type



- diffuse expansive sheets of cells with infiltrative borders and variable cellularity;
- tumor margins are more cellular
- hyperplastic synovium with papillary projections composed of foamy histiocytes and hemosiderin containing macrophages
- large clefts, pseudoglandular or alveolar spaces lined by synovial cells, osteoclast-like multinucleated (10 - 70 nuclei) giant cells, epithelioid cells

- abundant collagen may be present, but lymphocytes and plasma cells are sparse
- giant hemosiderotic granules (2 - 3x diameter of RBC), giant siderophages (Pathologe 2005;26:96)

- May have 5+ mitotic figures / 10 HPF, rarely chondroid metaplasia (Mod Pathol 2007;20:545)

- Malignant if nodular and solid invasive growth plus large cells with large nuclei, prominent nucleoli, necrotic areas and atypical mitotic figures

Differential diagnosis

- hemosiderotic synovitis
- associated with hemophilia and intraarticular bleeding,
- no mononuclear or giant cell nodular proliferation,
- hemosiderin primarily in synovial lining cells