Thymoma mimicking thyroid papillary carcinoma: another pitfall in fine-needle aspiration.

Thymomas are composed of a mixture of epithelial and lymphoid cells. When the lymphoid cells predominate, the possibility of malignant lymphoma must be considered. Recently, a thymoma mimicking lymphoblastic lymphoma was reported in this journal as a diagnostic pitfall in a mediastinal aspiration. We encountered another diagnostic pitfall at the other end of the spectrum: a thymoma with a dominant epithelial component in which a papillary carcinoma of thyroid had to be considered in the differential diagnosis.