Electronoptical aspects of the thyroid cold nodule.

The authors studied the ultrastructure of benign and malignant forms of the thyroid cold nodule. In the benign cold nodule the most striking feature was an irregular endoplasmic reticulum with large cisternae and scarce ribosomes, this meaning an impaired protein synthesis. Frequent lysosomes and phagolysosomes occurring in the apical zone of the cell were present. In the malignant form of the cold nodule, nuclear abnormalities, a reduced endoplasmic reticulum and a highly increased number of abnormal mitochondria were found. The increased number of mitochondria in the carcinoma is a compensatory reaction to the frequent abnormalities found in these organelles. No transitional ultrastructural stages could be established between benign and malignant cold nodules. In practice the nature of a cold nodule is established by thyroid surgery and histologic examination.