Pseudolymphoma of the thyroid.

An unusual case of pseudolymphoma of the thyroid is reported. The tumor was histologically characterized by good demarcation, mature lymphocytes with prominent follicle formation and germinal centers, and mature plasma cells. Immunohistochemical staining revealed a similar distribution of T- and B-cells to reactive lymph nodes and a polyclonal nature of the plasma cell infiltrate. These findings are closely related to the entity, pseudolymphoma in other organs. Differential diagnosis from follicular lymphoma or ectopic thymic tissue is discussed.