[Hemopigmented villonodular synovitis: ultrastructural study and a comparison with hemophiliac synovitis].

In a study of the ultrastructure of two cases of villonodular synovitis and two cases of haemophiliac synovitis, the authors observed very similar lesions. In both diseases, the lesions of the superficial layer of the synovium consisted of intermediate type (type C) synoviocytes loaded with iron pigments or lipid vacuoles. In the deep layer, the authors observed numerous macrophages loaded with siderosomes, lipid inclusions or phagocytosed red blood cells, giant cells and capillaries with a thickened basement membrane with a layered appearance. The cytoplasmic membranes of the synoviocytes were joined by desmosomes or filopodal digitations. The similarity of the lesions in the two diseases suggests a common histogenetic mechanism for the synovial lesions: chronic haemarthrosis.