Giant cell tumor of bone

Summary

We describe here the ultrastructure of the multinucleated giant cells and the mononuclear stromal cells in one case of giant cell tumor of bone. The most frequently occurring stromal cell (“stromal cell type 1”) was of fibroblast-like appearance with an irregular outline of both cells and nuclei. Characteristic features of the cytoplasm were the abundance of rough surfaced endoplasmic reticulum and the well developed Golgi apparatus; particulate glycogen was present in the ground cytoplasm of some cells. A second stromal cell type (“stromal cell type 2”) was also recognized, albeit more infrequently. It was macrophage-like with many mitochondria and lysosomes, but with a poorly developed endoplasmic reticulum.

The composition of the fixative was found to influence considerably the appearance of the multinucleated giant cells, especially of their endoplasmic reticulum and Golgi-associated structures. Vacuolar elements with taillike expansions were frequently observed in the vicinity of the Golgi apparatus; their functional significance and relationship to the Golgi apparatus and the endoplasmic reticulum is enigmatic. Bodies with the appearance of conventional lysosomes occurred in limited numbers — while mitochondria were abundant. The structural organization and distribution of the endoplasmic reticulum varied between different regions of the cells. Nuclei were of irregular shape with deep infoldings of their limiting membranes and peripheral condensation of the chromatin.

The possible nature of mononuclear cells in the neoplastic process is discussed. The morphologic evidence favors the conclusion that the fibroblast like stromal cell is neoplastic; convincing neoplastic properties are lacking for the type 2 cells. Although similarities exist between multinucleated giant cells and osteoclasts, distinct differences between the two cell types were noted. The origin, function and possible neoplastic nature of the giant cells is discussed on the basis of the findings presented.