Thymoma. A clinicopathologic study of 98 cases with special reference to three unusual cases.

98 thymomas were assessed in respect to clinical manifestations, gross and histologic pathological findings and clinicopathologic correlations. 34% of patients were asymptomatic and thymoma was detected fortuitously. The most common presenting symptoms were related to myasthenia gravis, symptoms due to pressure on mediastinal structures were next in frequency. The symptom-diagnosis interval ranged from 0 to 120 months with a median of 4,5 months and was longer in invasive thymomas (median 6 months) than in noninvasive thymomas (median 2 months). 52% of thymomas were encapsulated and showed no cytologic atypia and were therefore classified as benign encapsulated thymomas. 26% showed gross invasion of peripheral structures and 3% were thymic carcinomas on histologic grounds. Histologically 55% of thymomas were epitheloid cell type, 17% spindle cell type and 20% mixed type thymomas. Epidermoid type thymoma occurred in 3% of the cases. 3 cases showed some unusual morphologic feature: one was localized intrapulmonal, another had an outspread like a mesothelioma, and the third was a basaloid carcinoma with unusual goblet cell metaplasia. In the three cases immunohistological methods were used as a diagnostic tool. The lectins UEA-I, PNA and HPA and an anti-keratin allowed the diagnosis of epithelioma (in 2 cases) and showed some more cellular and structural differentiations (in 1 case).