Bethesda System Categories of Fine Needle Aspiration Cytology Are Not Associated with Thyroid Nodule Location: A Single Institution Experience

<b><i>Introduction:</i></b> Thyroid isthmus is defined as the thin band connecting thyroid tissue between both lateral thyroid lobes. Recently, a possible association between thyroid nodules located in the isthmus and malignancy was proposed. The aim of this study was to compare the frequency of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) categories between nodules from the isthmus and nodules from both thyroid lobes. <b><i>Methods:</i></b> All fine needle aspiration cytology procedures performed between January 2016 and December 2019 at the Pathology Institute of Araçatuba, São Paulo, Brazil, were analyzed. For each nodule, at least 2 conventional slides were produced (1 stained by Giemsa and the other by hematoxylin and eosin). All cases were reported according to the TBSRTC. Clinical information (gender, age, and localization) and ultrasound data (size of nodules) were collected from medical requisition forms. To assess the association between the frequency of TBSRTC categories and nodule location, univariate analysis was performed using the χ² test or Fisher’s exact test, as appropriate. A <i>p</i> value &#x3c;0.05 was considered statistically significant. Nodules located in transition between the isthmus and a right or left lobe were included in the isthmus group. <b><i>Results:</i></b> Considering the <i>p</i> value between the TBSRTC categories and thyroid nodule location, statistic association was not observed: nondiagnostic or unsatisfactory (<i>p</i> = 0.1442), atypia of undetermined significance or follicular lesion of undetermined significance (<i>p</i> = 0.3296), follicular neoplasm or suspicious for a follicular neoplasm (<i>p</i> = 0.0817), suspicious for malignancy (<i>p</i> = 0.8464), and malignant (<i>p</i> = 0.1082). <b><i>Conclusion:</i></b> In the studied population, nodules located in the isthmus were not related to any Bethesda System category.