A case of malignant mesothelioma containing intranuclear and intracytoplasmic inclusions

Background : Pleural effusion cytology has been suggested as a useful diagnostic tool in the early stages of malignant pleural mesothelioma (MPM). We report herein on a patient with MPM who presented with intranuclear and eosinophilic intracytoplasmic inclusions in pleural effusion cytology. Case : Left-sided pleural effusion was discovered in a 38-year-old woman without asbestos exposure on a routine medical checkup, and she was admitted. Computed tomography demonstrated thickening of the left pleura. During the follow-up period for pleural effusion, MPM was suspected based on the pleural effusion cytology findings. A diagnosis of MPM was made based on the immunocytochemical examination, using cytologic smear and cell block specimens, and electron microscopical examination of pleural effusion. A left parietal pleurectomy was performed, and the diagnosis of MPM was histopathologically confirmed. Cytological specimens of pleural effusion revealed malignant mesothelial cells containing numerous eosinophilic cytoplasmic inclusions and scattered intranuclear inclusions. Ultrastructurally, the intranuclear inclusions were made up of colloidal material surrounded by a single membrane. The eosinophilic intracytoplasmic inclusions consisted of an expanded rough endoplasmic reticulum and tubular structures forming whirl complexes of various sizes. Conclusion : Based on our findings, we conclude that examination of intranuclear and eosinophilic intracytoplasmic inclusions in mesothelial cells of pleural effusion cytology appears to be important in the diagnosis of MPM. Eosinophilic cytoplasmic inclusions in mesothelial cells may be of diagnostic significance for MPM.