RESUMEN

BACKGROUND: A fine-needle aspiration (FNA) biopsy is a basic procedure to verify the morphology of thyroid nodules. However, significant variations in the diagnostic performance of FNA, as well as fluctuations in the rate of malignancy (ROM) in different categories of the Bethesda System for Reporting Thyroid Cytopathology, have been discovered in many studies. The development and employment of additional molecular tests in daily clinical practice require an understanding of the prevalence and structure of thyroid malignancy in each category of the Bethesda system. METHODS: Current research is a continuous retrospective cohort study of the results of the examination and treatment of 1652 patients with thyroid tumors who have undergone primary surgery in 2021 at a national referral thyroid cancer center. FNA diagnostic performance was studied by comparing cytological diagnoses with histological outcomes. The authors evaluated ROM in each Bethesda category and identified the tumors representing a diagnostic pitfall. RESULTS: The overall ROM was 72.4%. When considering ROM in each Bethesda category, it was 16.7% in Bethesda I, 10.1% in Bethesda II, 23.0% in Bethesda IV, 74.8% in Bethesda V, 99.4% in Bethesda VI. The false-positive rate was 65.0%, false negative-0.67%. Follicular and oncocytic adenomas, as well as the follicular variant of papillary thyroid cancer, were the most troublesome entities for patients' management. CONCLUSION: ROM was comparable to the values implied by the Bethesda system. Follicular tumors were the main source of high false-positive rates. This necessitates the refinement of existing tests and the development of new diagnostic tests to overcome the abovementioned problems.