Reactive mesothelial cell and mesothelioma of the pleura

Summary

The results of a light and electron microscopic study and enzyme histochemistry of reactive mesothelial cells and diffuse and localized (solitary) pleural mesotheliomas were compared, in order to establish a diagnosis and elucidate the cell of origin of the mesotheliomas. The reactive mesothelial cells were usually regular in appearance but could be cuboidal or columnar, or even peg-shaped with large nuclei and prominent nucleoli. Colloidal iron and alcian blue staining were positive in the plasma membrane, microvilli and in parts of the cytoplasm of mesothelial cells. These stains were mostly negative following testicular hyaluronidase treatment. The neoplastic cells of diffuse pleural mesothelioma had some epithelial characteristics such as microvilli, desmosomes, and a prominent basement membrane and were similar to reactive mesothelial cells with regard to cellular form and staining for acid mucopolysaccharides. In this study the colloidal iron and PAS stains appeared to be more intense in mesothelioma cells than in reactive mesothelial cells.

In enzyme histochemistry, naphthol AS-D acetate esterase and α-naphthyl acetate esterase activity were demonstrated strongly in neoplastic cells. The nuclear-cytoplasmic ratio, the numbers of microvilli and mitochondria and the amount of glycogen were greater in the neoplastic cells when studied by electron microscopy. Electron lucent intracytoplasmic fibrils appeared wider and more distinct in mesothelioma cells.

Localized mesotheliomas, thought to be an entirely different entity from reactive mesothelial cells, showed little characteristic morphology in light microscopic pictures, few cytoplasmic organelles were seen ultrastructurally.