Cytological study of invasive thymoma and thymic carcinoma

We report the cytological characteristics of invasive thymoma and thymic carcinoma. First, left pleural effusion and an anterior mediastinal mass were found in a 62-year-old woman. Fine needle aspiration cytology showed cohesive clusters of epithelial cells and numerous scattered lymphocytes. Elliptical and polygonal tumor cells contained round and elliptical nuclei, fine aggregated chromatin and small nucleoli. The histological diagnosis was invasive thymoma. Next, an anterior mediastinal mass was found on medical examination. Metastatic liver cell tumors were detected by abdominal CT scan. Fine needle aspiration cytology showed scattered epithelial cells and lymphocytes. The nuclei were large and pleomorphic with coarsely granular chromatin and a few prominent nucleoli. The histological diagnosis was thymic carcinoma. Cytologically the differences between invasive thymoma and thymic carcinoma were pleomorphism of nuclei, increases in the N/C ratio and nuclear mitosis, coarsely granular chromatin and large nucleoli. It was difficult to determine the invasiveness of thymoma cytologically.