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Localized tumors of pleura should clearly be separated from diffuse pleural mesotheliomas due to clinical and pathological peculiarities. But there is some dispute on their proper interpretation and hence disagreement about their correct designation. Some call them "fibrous tumors (fibromas)" of pleura and appreciate by this term the fibroplastic potency of tumor cells and the lacking relation to overlying mesothelial surface cells, others prefer the name "fibrous mesothelioma" and allude to an at least abortive mesothelial differentiation within the tumor tissue. Examining 7 own tumor cases by means of light microscopic, topo- and immunohistochemical as well as electron microscopic methods the investigations were aimed at analysing the morphological structure of these tumors and subjecting it to a critical reappraisal with regard to a suited designation. Histologically, a marked variability of histological structure and texture was found, there were regions with similarities to fibromas, fibrous histiocytomas, hemangiopericytomas and nerve sheath tumors as well as blastema-like areas. Occasionally a vasoformative activity could be seen. In three tumors a few epithelioid cell complexes were visible, but neither keratin intermediate filaments nor UEA-I reactivity was to be demonstrated by immunohistochemistry. Antibodies against factor VIII associated antigen only marked endothelial cells of vascular structures. By the electron microscopic examination of 1 case abortive mesothelial differentiations were visualized (some lumen-like space formations, stub-like cellular projections of the cavity facing side, primitive intercellular junctions and fragmented basal lamina-like material). The findings inclusive the immunohistochemical results are discussed and jointly taken for sustaining the interpretation of these tumors as mesotheliomas and for militating against the classification as simple pleural fibromas or fibrous pleural tumors, respectively.

An Opton cytophotometer was used for a comparative morphometric study on mesothelial and tumour cells obtained from pleural effusions. Tumour cells coming from malignant neoplasms with epithelial or mesenchymal origin were measured. Slides stained after Ambs X Grönemeyer and Smetana methods revealing RNP structures have been used. Both methods were valuable for nucleolar morphometry but the technical simplicity of the second one made it preferable. Nuclear and nucleolar surfaces as well as diameters and perimeters of nucleoli have been studied. Nucleolar/nuclear index, i.e. average number of the nucleoli per nuclear profile as well as nuclear/nucleolar surfaces ratio have been counted too. A clear difference of the average nucleolar size in tumour cells compared to that of mesothelial ones was established. The count of nuclear/nucleolar surfaces ratio-reveals that nucleolar enlargement in tumour cells is higher than nuclear one. In constant changes in the nucleolar/nuclear index was revealed in tumour cells.

Two further cases of the so-called intravascular bronchioloalveolar tumour of lung are reported. Electron microscopic demonstration of Weibel-Palade bodies and immunocytochemical demonstration of factor VIII in the cytoplasm of the tumour cells indicate the vascular nature of these lesions. One patient presented with an enlarged liver and the tumour was found to be involving the liver and parietal pleura as well as the lung. The characteristic micropolypoid structure was not seen in the pleural or hepatic deposits and it is evident that this feature is a consequence of the alveolar architecture of the lung and is not an inherent property of the tumour.

Transmission electron microscopy has been found to be of greater value than scanning electron microscopy in the differential diagnosis of mesothelial reaction, malignant mesothelioma and metastatic carcinoma. It is possible to remove identified cells from slides for transmission electron microscopy, and this is particularly valuable when an urgent diagnosis is required.

Experimental mesotheliomas induced in albino rats by treatment with isometric crocidolite asbestos were studied by light and electron microscopy. The cellular structure of different types of neoplasms was examined. The ultrastructural investigation was carried out using both freshly-resected materials and those recovered from paraffin blocks. The characteristic features of nuclei and cytoplasm are described with special attention being given to cytoplasmic organelles. On the basis of morphological light and electron microscopic study the authors discuss the histogenesis of different types of mesotheliomas. An attempt is being made to establish the origin of fibromatous mesotheliomas and to improve the available classifications.

Waldenström's macroglobulinemia was diagnosed in a patient suffering from recurrent lymphocytic pleurisy. Ultrastructural studies of the pleura showed the features of Lennert's lymphoplasmacytoid immunocytoma. Computerized assisted tomodensitometry revealed a retroperitoneal growth surrounding the right kidney and squeezing the thoracic lymphatic duct.