[Ultrastructural diagnostic problems of pleural tumors. A study of 125 cases (author's transl)].

Ultrastructural studies may improve the diagnosis of pleural tumors. A comparative study of 125 primary and secondary pleural cancers provided the major structural features needed for differential diagnosis. Two cell types were always present in malignant mesothelioma: differentiated mesothelial, and fibroblastoid cells. The former had some features of metastatic epitheliomas (microvilli, microfilaments, junctional complexes, basement membranes). The later were specific. They were sometimes isolated, had the general aspect of fibroblasts but possessed typical microvilli. It was difficult to assess the diagnosis of malignant mesothelioma on isolated differentiated mesothelial cells in pleural fluids or biopsies. Cilia or secretory granules were found only in metastatic cells. The finding of fibroblastoid cells in a pleural tumor proves its mesothelial origin.