[Differential diagnosis of follicular neoplasm of the thyroid]

Fifteen resected follicular adenomas and 15 well-differentiated follicular carcinomas of the thyroid gland were analysed to determine whether a differential diagnosis of both "follicular neoplasms" can be performed by cytological criteria exclusively. 150-200 tumor cell nuclei (TCN) were studied per case for their TCN profile area, perimeter, density and for stereological estimates including the new parameter Vv, volume-weighted mean particle volume. Flow-cytometric analyses included measurement of the DNA index, the percentage of cells in S-phase and in G2/M phase. Follicular adenomas and follicular carcinomas did not show any significant differences in stereological estimates related to TCN size. Both groups included similar proportions of diploid and aneuploid neoplasms. Aneuploid follicular neoplasms showed a significantly greater area, perimeter and volume of TCN as compared to diploid tumors, regardless of their histological diagnosis. From our results a differential diagnosis of follicular neoplasms cannot be performed on the basis of cytological aspirates exclusively. Infiltration of capsula or vessels remain the only safe indicators of malignancy in the absence of metastases. The lack of cytological differences provides evidence that some follicular adenomas are preinvasive carcinomas, not yet showing infiltrative growth at the time of resection.