Interpretive Errors in Fine-Needle Aspiration of Thyroid: A 13-Year Institutional Experience in Lebanon.

Introduction: Fine-needle aspiration (FNA) is a worldwide established diagnostic tool for the assessment of patients with thyroid nodules. All thyroid FNA interpretive errors (IEs) were reviewed at the American University of Beirut Medical Center over a 13-year period, in order to identify and analyze them.

Materials And Methods: All FNAs and their corresponding pathology results are correlated yearly for quality assurance. Discrepant cases are segregated into sampling errors and IEs. All thyroid FNAs with IEs were collected from 2005 to 2017. FNA and pathology slides were reviewed by trained, board-certified cytopathologists, adhering to the latest Bethesda criteria. Reasons for erroneous diagnoses were studied.

Results: There was a total of 11 IEs out of 340 thyroid FNAs followed by surgical resection. Five benign follicular nodules (BFNs) were misinterpreted as suspicious for carcinoma. Focal nuclear atypia in cyst-lining or follicular cells and a monotonous population of macrophages misinterpreted as Hurthle cells (HCs) were the causes of IEs in this category. Four Hashimoto's thyroiditis (HT) cases were misinterpreted as suspicious for malignancy. Innate atypia of HCs and sampling misinterpretation were the causes of IEs in HT. One medullary and 1 follicular carcinoma were misinterpreted as suspicious for follicular neoplasm and BFN, respectively. Nine cases were better classified after review.

Conclusion: Thyroid FNA IEs can be mitigated by meticulous screening and identification of all elements on FNA smears. Awareness of focal nuclear atypia in reactive cyst-lining and follicular cells in BFN, as well as HCs in HT, is highlighted. Adherence to The Bethesda System for Reporting Thyroid Cytopathology and consulting experienced cytopathologists significantly decrease IEs.