Ectopic thymoma mimicking diffuse pleural mesothelioma: a case report.

A case of ectopic thymoma of the pleura with a particular growth pattern mimicking diffuse pleural mesothelioma is reported. Diagnostic imaging showed that the pleural tumor encased the entire left lung. The specimen biopsied from the tumor was composed of lymphocytes and epithelial cells, consistent with the mixed type of thymoma. The autopsy found no evidence of a mediastinal tumor. An involuted thymus was found in the parietal pleural tissue adhered to the apex of the left lung. The thymoma was thought to originate from the ectopic thymic tissue in the parietal pleura, as a lesion independent from the primary mediastinal thymoma, and spread along the pleura like diffuse mesothelioma.