The presence of siderosomes in synovioblasts (B cells) of chronic spontaneous hemarthrosis. Histologic, electron microscopic, and roentgenographic electron microanalysis studies of three cases.

The synovium of three patients with chronic spontaneous hemarthrosis was examined by light and electron microscopy and roentgenographic electron microanalysis. The synovium showed hyperplastic villous processes with proliferation of synovioblasts (B cells) and synovial macrophages (A cells). Erythrophagocytosis was observed in synovial macrophages but not in synovioblasts. Synovioblasts, however, had more numerous siderosomes than did synovial macrophages. Ferritin granules were identified in the cytoplasms of synovial macrophages and synovioblasts as well as in the intercellular space. It was noted that the longer the interval following the hemorrhagic episode, the fewer the siderosomes and erythrophagosomes in synovial macrophages. Therefore, it is likely that synovioblasts take up ferritin and/or inorganic iron released from synovial macrophages in chronic local iron overload.