Sections show a florid villonodular synovial proliferation with a dense, subsynovial infiltrate. The hypercellular stroma features a mononuclear population of small histiocyte-like cells and larger polygonal cells with eosinophilic cytoplasm. Multinucleated osteoclast-like giant cells and lipid-laden foamy macrophages are interspersed throughout. Prominent intra- and extracellular coarse hemosiderin deposition is present. The stroma exhibits focal fibrosis, cleft-like spaces, and peripheral extension into adjacent mature adipose tissue, lacking significant cytologic atypia, atypical mitoses, or necrosis.
The patient underwent an arthroscopic synovectomy of the left knee, with a tissue sample sent for histopathological examination to investigate a suspected diagnosis of Pigmented Villonodular Synovitis (PVNS).
Soft tissue fragments collectively measured 3x2.5x0.6 cm, totally embedded.