Diagnosis of thymoma by needle biopsy

One cutting needle biopsy specimen and six fine needle aspiration biopsy specimens of thymomas were studied in order to define diagnostic criteria for this entity in biopsy material. Two of the cases demonstrated a mixed pattern of epithelial cells and lymphocytes while epithelial cells predominated in four cases and lymphocytes in one. Tumors composed of a conspicuous admixture of benign-appearing epithelial cells and mature lymphocytes were easily diagnosed. Neoplasms composed primarily of one cell type also displayed distinctive cytologic features that correlated with the histopathologic appearance of the resected tumors and permitted a diagnosis. Immunocytochemical demonstration of keratin and T6 proved useful in confirming the biphasic pattern of epithelial cells and cortical thymocytes that is characteristic of thymoma.