[Morphometrical and immunohistochemical analysis of cortical and medullary thymoma: its correlation with invasiveness and association with myasthenia gravis].

Forty-seven thymomas were histologically classified to 28 cases of cortical type, 13 cases of medullary type, and 6 cases of mixed type. They were analyzed morphometrically and immuno-histochemically, and the results were examined with their invasiveness and association with myasthenia gravis (MG). Thirty-seven resected thymic tissues were used as controls. Cortical thymomas were more often invasive ones and associated with MG than the medullary type, with significant difference. Epithelial cell nuclei of the cortical thymomas were significantly larger than those of the medullary ones. Epithelial cell nuclei of cortical and medullary thymomas were significantly larger than those of thymic cortex and medulla, respectively. Morphometrical results showed that the cortical thymomas were more malignant than the medullary ones. Immunohistochemically, all cases of thymomas were positive for Leu7 and keratin, but stainability of them were variable among each subtype. In thymic tissues epithelial cells in outer cortex were positive for Leu7 and keratin, whereas those in inner cortex and medulla were negative for Leu7 and positive for keratin.