Bilateral pleural mesothelioma with large spherical and papillary clusters in pleural effusion: A case report: Bilateral MPM diagnosed by pleural cytology

Abstract

Malignant pleural mesothelioma (MPM) is uncommon, and bilateral lesions are particularly rare. We present a case of MPM with characteristic clusters diagnosed by the cytological examination of bilateral pleural effusion. A 52-year-old male with bilateral pneumothorax had a tumor shadow in the left pulmonary apex measuring up 25 mm by computed tomography. Thoracoscopic partial resection of the left lung revealed multiple plaques indicating tumor dissemination, and hemorrhagic pleural effusion in the left thoracic cavity. Intraoperative pleural cytology showed epithelioid mesothelial cells arranged in large spherical and papillary clusters, mixed with scattered sheetlike mesothelial cells with chronic background inflammation. Despite seeing small mononuclear mesothelial cells in the large clusters, we suggested MPM. Histopathologic examination revealed the proliferation of epithelioid tumor cells with glandular and tubulopapillary structures in the fibrous thickened visceral pleura and peripheral lung. Immunohistochemistry showed positive staining for calretinin, D2-40, and WT-1. The patient was diagnosed as having MPM. Later pleural cytology following thoracoscopic partial resection of the right lung again showed mesothelial cells in spherical and papillary clusters, which were also diagnosed as MPM. The large spherical and papillary clusters in the pleural effusion were critical to the cytological diagnosis of MPM.