The clinical effect of second needle aspiration and repeated cytological investigation for same thyroid nodule

Introduction: Thyroid nodules initially classified as Bethesda categories II, III, or IV are occasionally re-aspirated due to evolving clinical or ultrasonographic features, or as part of structured protocols. This real-world study aimed to (1) determine the frequency of changes in Bethesda classification following repeat fine-needle aspiration (FNA), (2) assess the relationship between Bethesda category shifts and the clinical indication for re-aspiration, and (3) evaluate malignancy rates in nodules that demonstrated cytologic reclassification. Methods: A retrospective analysis of thyroid nodules that underwent more than one FNA between 2018 and 2024. Only nodules initially categorized as Bethesda II, III, or IV were included. Cytological outcomes were compared between the initial and repeat aspirations. Results: A total of 429 nodules underwent repeat FNA, with 111 nodules meeting inclusion criteria. Among nodules initially classified as Bethesda II (benign), 40.4 % were upgraded to a higher Bethesda category on repeat aspiration. For nodules initially categorized as Bethesda III or IV, 13.6 and 21.6 % were upgraded, while 40.6 and 48.6 % were downgraded to a lower-risk category, respectively. Malignancy rates correlated with upgraded cytology classifications: 55.6–80 % of nodules reclassified as Bethesda III / IV were malignant, while 66.7–100 % of nodules upgraded to Bethesda V / VI were confirmed as malignant on final pathology. Conclusions: Repeat FNA of thyroid nodules - particularly when prompted by clinical assessment, sonographic changes, and institutional guidelines for indeterminate cytology - can significantly refine risk stratification. These findings support the high diagnostic utility of repeated aspiration in appropriate clinical scenarios.