Appearance of mesothelial cells in the bronchial brushing-A case report

Background: Although the appearance of mesothelioma cells in sputum have been well described, no cases with nonneoplastic mesothelial cells in the bronchial brushings have been reported to date. Case: A 66-year-old man presented with atelectasis and multiple giant bullae in the left upper lobe. Bronchial brushing was performed and normal mesothelial cells were observed associated with ciliated columnar cells and alveolar macrophages. The mononuclear mesothelial cells formed large sheets with clearly outlined cell borders. The mesothelial cells were uniform in size and configuration. They had grooved nuclei with finely granular chromatin and inconspicuous nucleoli. These cells were positive for HB: EM-1. The cytologic diagnosis was confirmed by histologic study of the excised lung biopsy specimens. Immunohistochernical examination of AE 1/AE 3 was positive on the visceral pleural mesothelial cells but EMA and vimentin were negative. The MIB-1 positive rate of these mesotheial cells was 0.2%. Conclusion: The cells were diagnosed as normal mesothelial cells on cytology, histology and immunohistochemistry. They were not reactive mesothelial cells because they had low proliferative activity. We concluded that these normal mesothelial cells were taken from the lung pleura.