Cytological and histopathological correlation of Bethesda 3 categories in thyroid cytopathology: a 4-year single-center experience

Aim:The aim of this study was to investigate the correlation between thyroid fine needle aspiration biopsy (FNAB) and thyroidectomy materials diagnosed as atypia of undetermined significance (AUS) with histopathological diagnoses over the last four years in our hospital. Materials and Methods:In this retrospective study, 251 thyroid FNAB cases who came to our laboratory between 01.01.2020 and 31.12.2023 with an AUS diagnosis and 133 patients who had operations in our hospital were included in the study. Results:A histopathological diagnosis was determined in a total of 133 cases, 94 cases after the first AUS diagnosis and 39 cases after at least one control aspiration.Of the 39 patients who underwent a second cytological control, 56.4%(n=22) were re-diagnosed with AUS. Of the surgical patients, 36.8%(n=49) were diagnosed with papillary microcarcinoma, 33.83%(n=45) with papillary carcinomas, 9.02%(n=12) with adenomatous hyperplasia and nodular hyperplasia, 6.7%(n=9) with invasive encapsulated follicular variant of papillary thyroid carcinoma, 3.75%(n=5) with follicular carcinoma, 3%(n=4) with chronic lymphocytic thyroiditis, 2%(n=3) with follicular adenoma, 1.5%(n=2) with well differentiated thyroid tumor of uncertain malignant potential, and 0.75%(n=1) each with medullary carcinoma, oncocytic carcinoma, anaplastic carcinoma-not otherwise specified, and paraganglioma. Because the majority(91.83%) of the cases diagnosed with papillary microcarcinoma were ≤5 mm in size and there were benign nodular structures in non-tumor areas, it was concluded that aspiration was performed from benign nodules and postoperative papillary microcarcinoma was detected incidentally. Conclusion:In our study, most of the patients diagnosed with AUS had a diagnostic operation by the clinician, and the patients who underwent repeat cytology were mostly re-diagnosed with AUS.It was remarkable that the majority(36.8%) of the patients diagnosed with AUS from an FNAB were diagnosed with incidental papillary microcarcinoma after resection. Since papillary microcarcinomas tumors are smaller than 1 cm, these cells are not sufficiently included in the cytology material from an FNAB.