Diagnosing malignant pleural mesothelioma.

The diagnosis of malignant pleural mesothelioma is a difficult clinical task. A suspicion of mesothelioma should always arise, when a patient with a case history of reasonable asbestos exposure is examined for pleural effusion or pleural masses of unknown aetiology [1]. In addition to asbestos exposure a heredilory predisposing factor has been suggested to be of importance for the development of malignant mesothelioma [2, 3]. Analyses of pleural fluid have been of limited value. The sensitivity of cytological examination of pleural nuid for detecting malignant mesothelioma has been low [4-6]. Elevated content of hyaluronic acid in pleural fluid is associated with malignant mesothelioma [6-8]. However, many mesotheliomas do not produce hyaluronic acid, and other causes of elevated hyaluronic acid content occur [7, 8). The morphological variability of the tumour is the main cause of diagnostic pro blems . Mal ignant mesothelioma ceUs are difficult to distinguish from benign reactive mesothelial cells [4, 5, 9]. Furthermore, malignant mesothelioma may morphologically mimic other neoplasms metastatic to the pleura, especially adenocarcinomas [6, 9]. These difficulties have made access to tissue specimens of crucial importance for a correct diagnosis. Reports have shown that thoracoscopy is signWcamly superior to cytology ([6, 10] or Abrams needle biopsy [10], and is almost as good as thoracotomy [10] for diag nosi ng meso the lioma. Pathologists, if offered an option, would still prefer thoracotomy due to the larger amount of tissue available for examination [9). InitiaUy the microscopic patterns of expression were classified as epithelial, fibrous-sarcomatoid and biphasic [11). RecenUy, this classification has been revised, and a great number of morphological patterns are now recognized. In a review of several reports, including a total of 819 cases of mesothelioma, 50% were of the epithelial tumour type, 16% were of the sarcomatoid type and 34% biphasic [12]. At least half of the epithelial mesotheliomas show morphological patterns which make a diagnosis of mesothelioma the most plausible. There are no diagnostic difficulties regarding the biphasic tumour type and seldom with the fibrous-sarcomatoid tumour type. An experienced lung pathologist using traditional stainings with the addition of stainings for mucosubstances (periodic acid-Schiff) and hyaluronic acid (Alcian blue(foluidine blue) should thus be able to