Cytopathology of thymoma

From 1967 to 1981, 37 cases were diagnosed as thymoma by transthoracic fine needle aspiration biopsy. All were verified histologically, with no false-positive results. The various cytomorphologic patterns of thymoma are presented. All aspirates from the thymomas were reviewed and found to be composed of epithelial elements, with an admixture of lymphocytes in various proportions. There were 13 cases of lymphocytic predominance, 11 of epithelial-cell predominance, 4 of spindle-cell predominance, and 9 of mixed cell types. In the cytologic preparations the epithelial elements from different tumors exhibited different cytologic appearances and were tentatively subclassified into five types: small, intermediate, large, large pleomorphic and spindle shaped. The cytologic features of thymoma observed in aspiration biopsies are sufficiently distinctive from those of other anterior mediastinal tumors to be diagnostic. It appears feasible to investigate an anterior mediastinal mass with percutaneous fine needle aspiration for the purpose of establishing the diagnosis of thymoma prior to median sternotomy or thoracotomy.