Pleural biopsy in the diagnosis of malignant mesothelioma.

In an attempt to distinguish reactive from neoplastic mesothelial proliferation, the histological material and clinical records of 153 patients on whom open or closed pleural biopsies were performed during 1976 were reviewed. In six of the 10 patients subsequently shown to have malignant mesothelioma the specimens from closed pleural biopsy had been reported as negative or equivocal but in retrospect showed changes not observed in reactive pleurisy. These included papillary mesothelial proliferation, exfoliated papillae, sheets of atypical mesothelial cells, and abnormal fibroblastic proliferation. In contrast, in inflammatory conditions the mesothelial lining was usually replaced by granulation tissue, although sheets or clumps of exfoliated mesothelial cells were often present in the corresponding pleural fluid clot. Some multilayering of parietal mesothelium was occasionally seen in chronic pleurisy and around metastases.