Cytologic detection of malignant mesothelioma of the pericardium

We have reported a very rare case, malignant mesothelioma of the pericardium, with the initial diagnosis made by cytology from the smears of the pericardial fluid. There were numerous large clusters in the smears, in which two types of cells were mixed: adenocarcinoma-like round cells and fibrosarcoma-like spindly cells. Some round cells very much resembled benign mesothelial cells. Central collagenous stalks and brush borders with long microvilli in the round cell aggregates were specific for carcinomatous mesothelioma and differentiated the round cells from adenocarcinoma cells. On the other hand, the spindly and pleomorphic tumor cells, present both singly and in clusters, implied malignancy. Therefore, a preliminary cytologic diagnosis of probable mixed malignant mesothelioma was made. Histopathologic and electron microscopic examinations confirmed the cytologic description that this tumor was a malignant mesothelioma.