Ultrastructure of thyroid tumors. 1. Follicular adenomas and carcinomas in rats and hamsters

The ultrastructure of experimentally induced thyroid follicular adenomas and carcinomas was studied in rats and hamsters by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Diaminobensidintetrachlorid (DAB) method was applied for cytochemical demonstration of the thyroid peroxydase activity. No significant difference was found in the ultrastructure between thyroid follicular adenomas and carcinomas in rats and hamsters. However, the ultrastructural organisation of tumor cells in carcinomas presuppose a more limited functional activity than in adenomas. The peroxydase activity of tumor cells was preserved, despite the presence of methylthiouracil (MTU) in the circulation. It was further noticed that malignant transformation of thyroid follicular cells does not lead to changes in the ultrastructural distribution of peroxydase activity. Scanning electron-microscopical examination of the thyroid tumors reveals significant changes in the structural organisation of tumor cells and follicles. The changes in the surface properties of thyroid gland in the course of malignant transformation should be considered as result of irregular cell proliferation, degenerative processes and functional heterogeneity of tumor cells.