Qualitative distinctive differences between the vacuoles of mesothelioma cells and of cells from metastatic carcinoma exfoliated in pleural fluid.

The qualitative features of the intracytoplasmic vacuoles occurring in the cells of pleural malignant mesothelioma and of metastatic carcinoma exfoliated in pleural fluid were studied. There were important differences in the two types of vacuoles. In mesotheliomas, the vacuoles were centrally situated, small and regular in size; these vacuoles stained positively with fat stains and always negatively with the periodic acid-Schiff stain. In routine cytology, these lipid-containing vacuoles can best be seen in air-dried May-Grünwald-Giemsa-stained smears and are almost invisible in wet-fixed Papanicolaou-stained smears. In metastatic carcinoma, the vacuoles were irregular in size, noncentral in location and often positive with mucin stains. Electron microscopy was used in one case to further elucidate the staining patterns of the vacuoles. This study proves that the analysis of the qualitative features of vacuoles of malignant cells exfoliated in pleural fluid can be of great value in the distinction between metastatic carcinoma and mesothelioma.