Fine needle aspiration cytology of thymoma

Thymoma is the 2nd most common mediastinal tumor found in Thai people. Cytologically it has a characteristic biphasic cell pattern and can be differentiated from other mediastinal lesions. We reviewed 14 aspirated samples, initially diagnosed as thymoma among a total of 80 mediastinal aspirations, obtained during a period of 6 years. Revised cytologic diagnosis was made and compared with histopathology from needle biopsy, surgical biopsy and surgical removal in each case. All cytologic samples revealed a mixture of epithelial cells and lymphocytes in varying proportions. Histopathologic samples were available in 13 patients and showed 12 thymomas and 1 immature teratoma. While all thymomas revealed characteristic cytologic features, a case of mediastinal immature teratoma with unsatisfactory aspirated sample revealed resembling features and it was very difficult to differentiate such a tumor from thymoma.