Fig. 6

Photomicrographs of H&E stain samples, which were taken from the resected mass in poplitea (a1–3), the proliferated synovial tissue in the knee (b1–3) and the lesion in the patella (c1–3), respectively. Low power views (a1, b1, c1; ×40) are characterized by a prominent number of epithelioid cells with fibrous stroma. Medium power (a2, b2, c2; ×100) views demonstrates numerous mononuclear cells, scattered multinucleated giant cells and occasional cytoplasmic hemosiderin. Under higher magnification (a3, b3, c3; ×200), the mononuclear cells are round or spindled and they have minimal cytoplasm and eccentric nuclei. There are some foam cells. Some cells typically contain cytoplasmic hemosiderin granules. No mitotic figures and atypia were found. The pathological features of the lesions from different locations are very similar to one another. Histologically, all findings consistently confirmed the original diagnosis of PVNS