Fine-needle aspiration cytology diagnosis of colloid nodule versus follicular variant of papillary carcinoma of the thyroid.

The cytologic differential diagnosis of colloid nodule (CN) and the follicular variant of papillary carcinoma (FVPC) is difficult with common morphologic features. To assess the utility of 18 cytologic morphometric parameters in the diagnosis of these thyroid lesions we evaluated 31 FNA samples that had histologic confirmation of the diagnoses. These 31 cases included 15 cases of CN, 8 cases of FVPC, and 8 cases of the usual variant of papillary carcinoma (UVPC) for reference values. For the morphometric analysis we used an Optimas 4.0 image analysis system. Comparing the CN group with the UVPC group revealed that eight of the parameters had statistically significant differences. The UVPC specimens were more cellular, less cohesive, had presence of papillary cellular groups more frequently, larger nuclei (UVPC: 109.33 +/- 30.19 microns2; CN: 66.81 +/- 15.02 microns2), higher nuclear to cytoplasmic (N/C) ratio, larger nucleoli, and present nuclear grooves and nuclear pseudoinclusions more frequently. The FVPC group differed from the CN group only in three parameters which included larger nuclei (98.49 +/- 18.24 microns2), higher N/C ratio, and a more frequent presence of nuclear pseudoinclusions. When we compared these two variants of papillary carcinoma, we found that the UVPC specimens had less cellular cohesion, less preservation of the architectural polarity and a more frequent presence of papillary cellular groups than the FVPC. The FVPC can be differentiated from CN based on nuclear changes, which included a larger size, higher N/C ratio, and presence of pseudoinclusions. The absence of cellular cohesion and polarity combined with the presence of papillary groups are useful in separating the UVPC from the FVPC. A cutoff of 75 microns2 should be used in separating benign from malignant nuclei.