Soft Tissue, Diffuse-type giant cell tumour

Diffuse-type giant cell tumour (formerly “pigmented villonodular synovitis”) is a joint disease related to inflammation causing a clonal proliferation of synovial-like cells. It typically affects the hip and knee joints but can also occur in the joints of shoulders, hands, elbows, ankle, and foot. The knee is the most common. Sections show a cellular lesion with a vaguely nodular architecture, composed of a heterogeneous population of cells including large epithelioid cells with abundant eosinophilic cytoplasm and vesicular round to oval nuclei, multinucleated osteoclast-like giant cells, hemosiderin-laden macrophages, and foamy macrophages. There is a focal area of necrosis and scarring. An iron stain reveals hemosiderin deposition within the soft tissue and macrophages.