Herein, we report a case of micronodular thymoma with lymphoid stroma in a previously healthy 73-year-old male. Thymectomy was performed. The solid and macrocystic masses were encapsulated with focal invasion. The solid portion consisted of nodules of bland-looking spindle or round epithelial cells in lymphoid stroma containing prominent germinal centers. The epithelial cells had moderate amount of cytoplasm and occasional mucin production. The cystic portion was lined with cuboidal epithelium. According to World Health Organization (WHO) classification, the mass was diagnosed as a micronodular thymoma with lymphoid stroma accompanied by a pre-existing multilocular thymic cyst. Micronodular thymoma with lymphoid stroma, a possible variant of type A thymoma, is an extremely rare tumor. This so-called "unusual" variant may imply the schematic weakness of the current WHO classification that cannot cover all morphologic types. Further study is recommended for clarification of this variant and its incorporation into the current classification.

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