PRIMARY PLEURAL THYMOMA

An unusual thymoma is reported in a 32-year-old woman. The tumor prese nted as diffuse pleural thickening with encasement of the left lung. C omputed tomographic scan and pleural biopsy of this pleural-based lesi on were interpreted as favoring a diffuse pleural mesothelioma. After pleuropneumonectomy, pathologic examination revealed a characteristic epithelial thymoma. However, neither mediastinal involvement nor a con current mediastinal mass was found at surgery or by radiographic exami nations. To our knowledge, only six previous cases of thymomas have be en reported as pleural-based tumors for which a mediastinal origin cou ld be excluded (namely primary pleural thymomas). It is emphasized tha t in clinical and pathologic diagnosis of a pleural-based lesion thymo ma should be considered in the differential diagnosis.