Atypical glycogen deposits in a plasmacytoma: An ultrastructural study

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Abstract
A solitary, benign plasmacytoma, arising from the gum of the lower jaw of a dog, was studied by light microscopy and EM. Some of the tumor cell nuclei showed the characteristic clockface or cartwheel pattern of heterochromatin distribution similar to that found in normal plasma cells. Like normal plasma cells the tumor cells were well endowed with rough endoplasmic reticulum but this was invariably dilated or vesiculated. Glycogen deposits were found within mitochondria and the dilated and vesiculated rough endoplasmic reticulum. The idea that these deposits were derived secondarily from glycogen deposits in the cytoplasm seems untenable because no glycogen particles were found in the cytoplasmic matrix. It would appear that most, perhaps all, stages of glycogen synthesis occurred within the mitochondria and rough endoplasmic reticulum of some of these tumor cells.