Value of quantitative nucleolar features in the preoperative cytological diagnosis of follicular neoplasias of the thyroid.

Nucleolar prevalence, size, and outline were investigated on cytological material from cold thyroid nodules obtained by fine needle aspiration. The percentage of nucleolated nuclei in follicular adenoma (32 cases) was less than in follicular carcinoma (26 cases). In adenoma most nuclei contained one nucleolus, and nuclei with two or more nucleoli were less common than in carcinoma where most cases showed the highest nucleolar diameter values. There was some overlap between adenomas and carcinomas, however, when the mean of the 10 largest values of the major nucleolar diameter was considered. In follicular carcinoma the percentage of marginated nucleoli--that is, those touching the nuclear membrane--was, in general, greater than 20%; in adenoma the values were equal to or lower than 16%. The overlap index showed that the percentages of marginated nucleoli and nucleolated nuclei are the two best discriminatory features between adenoma and carcinoma.