[Pleural mesothelioma: morphology, histochemistry, difficulties in diagnosis and nosologic problems (author's transl)].

Using the material of the French Register, these authors define the epithelial aspects and the histological forms of diffuse pleural mesothelioma. Histochemistry studies, on pleural cytology and on tissues, are of the utmost importance in distinguishing mestothelioma from carcinoma. Hyaluronic acid is almost always showed in the epithelial mesothelioma, being otherwise only noticed in some very flourishing forms of mesothelial cell hyperplasia nad in rare mucus-secreting carcinoma. Cytoenzymology studies are very useful on pleural fluid material, making it possible to show the difference between macrophages and mesothelial cells. Difficulties encountered by pathologists are analysed with reference to the materials examined: cytology, needle biopsy, guided biopsies, surgical material and documents from autopsies. After a critical study of the structures seen in other pleural tumors mesothelioma is defined as a localized or diffuse tumor of the pleura, positively originating from mesothelial cells which manifest either epithelial structures of a double epithelial and mesenchymal composition.