An electron microscopic study of calcification of retinoblastoma.

We examined three eyes with retinoblastoma that had clinical evidence of calcification. The light and electron microscopic study of the retinoblastoma cells from these eyes disclosed an intramitochondrial calcium deposition after plasmalemma disruption. Morphologically, calcium deposits initially occur as needle-like structures gathered within the mitochondrial membrane. With progressive necrotic liquefaction of tumor cells, microbodies develop a central calcified cone surrounded by an electron-translucent zone with coarse needle-like calcium deposition on the surface.