Hyperthyroidism-Related Epithelial Hyperplasia as a Potential Pitfall of Thyroid Cytology: Institutional Cytomorphological Analysis of Histologically Verified Cases

Introduction: Hyperthyroidism-related epithelial hyperplasia is seldomly listed as a pitfall in thyroid cytology. Therefore, we focused on the cytomorphological characteristics of epithelial hyperplasia and compared these features with papillary thyroid carcinoma (PTC). Methods: Study group consisted of 76 patients (133 FNA specimens) histologically diagnosed with hyperthyroidism-related epithelial hyperplasia without a concomitant malignancy. The control group contained 21 histologically verified FNAs of PTCs. A total of 48 cytomorphological features were quantitatively evaluated. Results: Statistically significant differences between the study groups were discovered on the architectural, cellular, and nuclear levels. Nuclear features varied most: nuclear elongation, grooves, irregular nuclear membrane, pseudoinclusions, the presence of nucleoli or small eccentric nucleoli were clearly more common in PTC group. Conclusion: Fine-needle aspiration referrals with clinical data and thyroid function test results can facilitate the interpretation of cytomorphological features and reduce the use of undetermined categories in cases of hyperthyroidism-related epithelial hyperplasia.