Usefulness of cellblock preparation in fine needle aspiration for the diagnosis of thyroid nodules

Background Thyroid nodules are common in the general population. The current diagnostic method for nodules is the ultrasound guided fine needle aspiration (US-FNA). The aim of the study was to evaluate the usefulness of cellblock preparation in addition to routine US-FNA in the diagnosis of thyroid nodules. Methods A retrospective study of patients with thyroid nodules submitted to US-FNA, with collection of material using both smears and cellblock preparation. Two air-dried smears were prepared for each nodule. After centrifugation, the residual aspirate in the syringe and needle was processed as a standard histology specimen (cellblock). Then a pathologist reviewed the smears and cellblock slides of each case. Results A total of 12.360 thyroid nodules were submitted to US-FNA. Cellblock preparation was performed in 153 (1.2%) in addition to smears. Among the satisfactory cellblocks (80.5%, 120), 31.7% (38) provided additional morphological information in comparison with smears alone. No significant differences were found between the smear and the combined smear and cellblock evaluation concerning the number of unsatisfactory (12.1% vs. 11.4%, p = .85) and indeterminate (27.5% vs. 24.2%, p = .52) results. Overall, 10 samples (6.7%) had their diagnosis changed after cellblock evaluation, nine of them due to immunohistochemical studies. Immunohistochemistry confirmed parathyroid origin of the nodule in six cases. Conclusion Cellblocks did not contribute to increase cellularity of the samples or to reduce indetermined results of FNA of thyroid nodules. Immunohistochemistry was essential to characterize rare cases without follicular histogenesis. Cellblock must only be prepared when considering performing immunohistochemistry.