The correlation of fine needle aspiration biopsy of the thyroid and post thyroidectomy histopathology results and the incidental malignancy rate

Thyroid nodules are the most common thyroid condition, and differentiating between benign and malignant nodules is a crucial step in the evaluation process. To make this distinction, fine needle aspiration biopsy is considered the gold standard. The aim of the study is to evaluate the correlation of the Bethesda classification used in histopathological assessment of fine needle aspiration biopsy and to assess the malignancy rate in nodules that do not present a clinically or radiologically suspicious appearance, and therefore, do not undergo fine needle aspiration biopsy. In this study, patients who underwent thyroidectomy at the Department of General Surgery, Akdeniz University Hospital, between 2020 and 2024, after a surgical decision was made in a multidisciplinary endocrine surgery council, were retrospectively evaluated. The patients' demographic information, preoperative and postoperative laboratory values, the sizes and biopsy results of nodules that underwent preoperative fine needle aspiration biopsy, postoperative tumor sizes, final pathologies, the sizes of nodules that did not undergo biopsy, and postoperative malignancy rates were examined. In the study, of the 521 patients evaluated, 366 (70.4%) were women and 155 (29.6%) were men. The age group distribution was as follows: 155 patients (29.7%) in the 18-40 age group, 250 patients (48%) in the 41-60 age group, and 116 patients (22.3%) in the 61-80 age group. According to the preoperative Bethesda classification, benign results were more common in Bethesda groups 1, 2, and 3, while malignant results were significantly more common in Bethesda groups 4, 5, and 6 (p<0.001). Among benign pathologies, follicular nodular disease was more common, while among malignant pathologies, papillary thyroid cancer was more common (p<0.001). In the study, the malignancy rate in Bethesda groups 1, 2, 3, and 4 was found to be higher than the standard classification, and in groups 5 and 6, the classification showed a correlation. The incidental malignancy rate detected in postoperative histopathological examination of nodules that did not show clinically or radiologically suspicious findings was 18.8%. Although preoperative fine needle aspiration biopsy results for patients with Bethesda 5 and 6 correlate with the classification, our study found a higher than expected malignancy rate in other groups. Therefore, patients who may require re-biopsy based on preoperative fine needle aspiration biopsy results should be closely monitored. The incidental malignancy rates detected in nodules that do not show clinically or radiologically suspicious findings are considerable, and in patients undergoing lobectomy for either benign or malignant reasons, the contralateral lobe should be thoroughly examined