Ectopic pleural thymoma in a 49-year-old woman: A case report.

Ectopic pleural thymoma is an exceedingly uncommon clinical entity that has only been described sporadically. Because of their peculiar location and variety of histologic patterns manifested, pleural thymomas may be confused with other neoplasms and may cause diagnostic problems clinically, radiologically, and morphologically. We describe the case of a giant left-sided ectopic pleural thymoma, preoperatively suspected to be a solitary fibrous tumor. A complete surgical resection was achieved and a postoperative diagnosis of WHO Type AB, modified Masaoka stage I tumor was attained. Subsequent thymectomy demonstrated unremarkable thymic tissue. The possibility of ectopic thymoma should be considered when the morphology of the lesion reveals a dual population of epithelial cells without significant nuclear atypia and lymphoid cells. Immunohistochemical studies are helpful in supporting the morphologic impression, both by characterizing the epithelial component as thymic in origin and by demonstrating the immature T-cell phenotype of the admixed reactive lymphocytes.