Pulmonary cytopathology of an invasive thymoma.

The cytopathology of an invasive thymoma that penetrated the bronchus is presented. As is typical of these neoplasms histologically, both epithelial cells (thymocytes) and lymphocytes were seen cytologically. However, the benign appearance of the thymocytes precluded a neoplastic diagnosis initially. Only with the knowledge that an anterior mediastinal mass is present roentgenographically can this diagnosis be safely made cytologically.