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Thoracoscopy with a single opening was carried out under general anesthesia with a cold light thoracoscope of 7 mm in diameter. Biopsies were taken under visual control for optical and electron microscopic examination. In a series of 40 mesotheliomas, 30 patients with pleural effusion underwent 36 thoracoscopies. In 29 patients the macroscopic lesions were compatible with the diagnosis of mesothelioma. The most specific aspects consisted in white-yellowish nodules, almost translucent, arising from the parietal pleura (9 patients). Another typical pattern, a dense pleural thickening, was found in 10 patients. In the remaining patients, the lesions observed were less specific. The biopsy was positive in 35/36 thoracoscopies (97%). A talc poudrage was carried out in 10 patients: their mean survival was 458 days. In ten matched mesothelioma patients who underwent pleurectomy the mean survival was only 395 days. In 12 patients at an early stage, the visceral pleura was not involved by the tumor: their mean survival was 636 days. In 11 patients both parietal and visceral pleura were involved by the tumor: their mean survival was 138 days: (p less than 0,001). It is concluded that in mesothelioma pleural effusions, thoracoscopy is a safe and efficient procedure in order to reach a precise diagnosis, prognosis and efficient palliative treatment of the effusion.

The problems of the anatomo-pathological diagnosis of pleural mesotheliomas are analysed on the basis of macro- and microscopic findings. It is emphasized that histological diagnosis rests above all on the structural polymorphism of the mesothelioma and presents considerable difficulty. It is considered that systematic examinations with the electroni microscope should pave the way to more accurate diagnoses of this tumour.

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.

Sixteen cases of malignant mesothelioma (13 pleural and 3 peritoneal) are reported. Fifteen cases were autopsied; in one case only biopsy material was available which are studied by electron microscopy. Among the autopsy cases, 12 had had previous biopsies, one had undergone multiple cytological examinations and 2 cases only one cytological examination. It was concluded that clinical signs and symptoms of mesothelioma were not specific and did not allow the diagnosis. For differential diagnosis as between mesothelioma and metastatic carcinoma, biopsy seemed to be more reliable that exfoliative cytology. Alcian blue stain after hyaluronidase digestion is a reliable test in the diagnosis of mesothelioma only when alcian blue is positive initially. However, in half of our mesothelioma cases this stain remained negative. Electron microscopic study appeared to be a satisfactory method of differentiating between malignant mesothelioma and metastatic carcinoma.