Introduction:
The nuclear features that are thought to be classic indicators of thyroid nodules are not fully observed in core needle biopsies (CNB). The aim of this study was to evaluate the histopathological differences between CNB samples and resection sections.

Material and methods:
The haematoxylin and eosin-stained CNB and resection sections of thyroid nodules were retrospectively re-evaluated in terms of nuclear and architectural parameters. The evaluations were conducted by 2 pathologists. Statistical analysis was applied in 80 selected cases diagnosed as benign (n = 37) and papillary carcinoma/suspicious for papillary carcinoma (n = 43).

Results:
The nuclear findings in the CNB were more subtle than in the resection sections. The nuclei were smaller (measurements of the nuclear areas, major axes, and minor axes in CNB and resection sections were 52.62 µm2, 9.89 µm, 6.75 µm, 129.18 µm2, 14.53 µm, and 10.79 µm, respectively). Hypochromia was detected in 46.5% of the papillary carcinoma cases. Grooves and pseudoinclusions were the other nuclear features that could be detected. However, nuclear contour irregularity was the most reliable finding that could predict papillary carcinoma diagnosis in the CNB sections (v: 0.82, p < 0.001).

Conclusions:
We believe that the histopathological differences we found have an important place in diagnostics and should be emphasized, and new diagnostic algorithms should be developed.