Proliferation, polymorphism and papillary hyperplasia of the follicular cells and endothelial cells can be often observed on the benign structural background of the thyroid follicular adenoma and this makes it difficult to find out the malignancy with Ught microscopy (1,2,3). The ultrastructural anaplastic changes of the cells and organelles called our attention. Recently some of the authors think that any papillary change in thyroid is the evidence of malignancy.

Twenty cases with follicular adenoma, ten cases with papillary carcinoma of the thyroid diagnosed with light microscopy were re-evaluated with electron microscopy in classical methods. In papillary carcinoma cases anaplastic changes of the tumour cells was showed ultrastructurally (Fig 1). Two of them, with no capsular or vascular invasion observed with Ught microscopy, there were proliferation of the microvilli in the apical parts of the thyrocites, and papiUary projections observed obviously. There were cystic dilations in cytoplasm and a lot of indentations of the nuclei.