Comparison of Cytological, Histopathological, and Imaging Findings Based on 10 mm Threshold in Pediatric Thyroid Nodules

<b>Background/Objectives</b>: Both benign and malignant thyroid lesions present as nodules. While thyroid nodules are less common in the pediatric population than in adults, their malignancy rates are considerably higher. Although the 10 mm cut-off for fine-needle aspiration cytology (FNAC) is commonly used for both adults and children, there is limited information regarding subcentimeter thyroid nodules in the pediatric population. The majority of published studies have focused on nodules measuring 1 cm or greater. This study aimed to compare the cytological diagnosis, ultrasonographic features, and histopathological outcomes of thyroid nodules in pediatric patients (under 21 years old), stratified by size (≤10 mm vs. >10 mm). <b>Methods</b>: We conducted a retrospective, single-center cohort study, evaluating 108 thyroid nodules from 98 patients. Nodule sizes were categorized into two groups, and their features were correlated with findings from FNAC using the Bethesda System for Reporting Thyroid Cytopathology and subsequent surgical histopathology. The risk of malignancy (ROM) was calculated for each Bethesda category. <b>Results</b>: A total of 108 nodules were evaluated, with 35 (32.4%) measuring ≤ 10 mm. The overall malignancy rate was 12%, with 14.3% in the ≤10 mm group and 11% in the >10 mm group. The difference was not statistically significant, and this finding indicates that small nodules can also harbor malignancy. Notably, all cases categorized as suspicious for malignancy or malignant by FNAC were confirmed to be malignant on histopathology (ROM = 100%). The Atypia of Undetermined Significance (AUS) category exhibited a malignancy rate of 60%, which is significantly higher than the rates reported in previous studies. Ultrasonographic features such as hypoechogenicity and microcalcifications were more prevalent in malignant nodules but lacked statistical significance. <b>Conclusions</b>: Our findings demonstrate that pediatric thyroid nodules, including those ≤10 mm, have a notable risk of malignancy. The high rate of malignancy in the AUS category suggests that the current Bethesda criteria, primarily designed for adults, may require re-evaluation for pediatric cases due to known differences in genetic profiles and disease behavior. Consequently, these pathological findings clearly demonstrate that FNAC indications in children should not be based solely on nodule size, and that a multidisciplinary approach guided by pediatric-specific guidelines should inform clinical management.