Discrimination between primary pleural and primary peritoneal mesotheliomas by morphometry and analysis of the vacuolization pattern of the exfoliated mesothelial cells.

Cells exfoliated from primary pleural mesotheliomas differ significantly from those from primary peritoneal tumors. In a quantitative study, it was shown that the pleural cells have larger nuclei, a more pronounced anisokaryosis and a higher nuclear-cytoplasmic ratio and, therefore, appear more malignant than the peritoneal cells, which have abundant cytoplasma and small nuclei. The differences in quantitative parameters were due to a more extensive vacuolization and consequent cytoplasmic distension, combined with nuclear compression in the case of peritoneal mesotheliomas. The morphometric parameters and the vacuolization patterns of cell populations in cases with both pleural and peritoneal involvement correlated with the data of the primary tumor regardless of the fluid in which the cells were found. This finding indicates the transcoelomic metastatic properties of malignant mesothelioma.