Discrimination between follicular adenoma and follicular carcinoma of the thyroid: preoperative validity of cytometry on aspiration smears.

The aim of our study was to evaluate the validity of the quantitative analysis of nuclear features on aspiration smears in the distinction between follicular adenoma and follicular carcinoma. Karyometric and DNA features, including the nucleolar count, were evaluated on the cytologic material of 28 cases; the values were in general slightly higher in the carcinomas than in the adenomas, with overlap between the two diagnostic groups. By plotting the two most discriminant and least correlated parameters against each other and by drawing two straight lines (one perpendicular to the axis representing the mean of the major nuclear diameter at the 9-microns point, the other perpendicular to the axis of the percentage of nucleolated cells at the 75% point), we obtained two regions: a rectangle delimited by the two axes and the two lines containing 86% of adenomas, and the remaining part of the plane containing 79% of carcinomas. The validity of this approach was tested in 32 new cases not included in the original bivariate classification: accuracy 87%; sensitivity 86%; specificity 88%; predictive value of adenoma 88%; predictive value of carcinoma 85%. In conclusion, a simple cytometric method, i.e., the combined evaluation of the mean of the major nuclear diameter with the percentage of nucleolated nuclei, allows a substantial distinction to be made between follicular adenoma and carcinoma.