Malignant synovioma: Electron microscopical findings in three patients and review of the literature

Abstract

Ultrastructural findings in 3 malignant synoviomas are described. Two typical biphasic tumors contained epithelial cells possessing filopodia or microvilli, specialized cell attachment and a basal lamina, and smaller stromal cells showing transitions to fibroblasts. In 1 case, the microvilli included fibrils resembling those in epithelial cells of the intestine and renal tubules. The 3rd tumor was spindle celled with little epithelial differentiation and no clear division into cell types, but intracytoplasmic microfibrils were conspicuous, forming ovoid masses. The tumor cells differ from normal human synovial cells but some of the features of the neoplasm are found in inflamed human synovium and normal synovial membranes of other species. The cytoplasmic fibrils in the 3rd case are similar to those reported by others in epithelioid sarcoma, a tumor that may be of related origin to synovioma. The phenomenon may be degenerative.