Malignant mesothelioma of the pleura.

Primary mesothelioma of the pleura is a controversial entity referring to a growth originating from the mesothelium, the cell layer covering the inner surface of the pleural, pericardial and peritoneal cavities which are derived from the celomic space of the embryo. Willis1 denies their existence entirely and considers isolated masses of the pleura as rnetastatic deposits of some distant asymptomatic primary focus. Anderson believes that in most instances neoplastic involvement of the pleura originates from a bronchial cancer, but he admits that in a small number of cases no intrapulmonary growth can be detected with a most meticulous examination. Ackerman and del Regato3 are convinced that primary pleural mesothelioma exists but consider it a rare disorder. It may be benign appearing as a fibrous mass or malignant showing alveolar, follicular or papillary patterns. Even the latter types have a tendency to remain localized and to expand by invasion of the neighboring structures rather than by distant metastases. However, metastases do occasionally occur into almost any part of the body. Undoubtedly, benign primary tumors of the pleura have been repeatedly recognized ;4.9 therefore, the controversy between the various pathologists must refer to the malignant types which are difficult to classify on account of the great variability of their microscopic appearance.4-12 These may be localized tumors varying from coin lesions13 to huge masses occupying one hemithorax, or they may appear as diffuse thickening of the pleura with or without effusion. Their consistency varies from soft to hard, from brittle to elastic; their color has been described as white, grey, yellow, orange, red, or bluish. Their microscopic picture may resemble carcinoma, endothelioma, epithelioma, sarcoma, fibroma, fibromyoma and giant cell tumor. Stout and Murray’#{176} believe to have solved the puzzle of the variable appearance of these tumors by demonstrating in tissue cultures that mesothelioma cells can develop into solid, tubular, or glandular structures of epithelial character as well as into mesenchymal tissues with fibroblasts, collagen, and reticulum fibers. Sometimes one form of growth predominates but more often there is a mixture present causing a great variability of different sections of the same tumor. Other authorities,2 however, are of the opinion that bronchogenic cancers may reveal all the pathological features described as characteristic of mesothelioma. This confused status of the pathology of pleural tumor masses makes their clinical evaluation difficult and is apparently responsible for the scarcity and brevity of reports describing their symptomatology during lifetime which is in contrast to the extensive literature discussing their autopsy appearance. Nevertheless, the practicing physician will have to face from time to time the problem of dealing with such isolated pleural growth deserving the