Risk of malignancy in thyroid nodules classified as Bethesda categories III, III - subcategories and IV: 2.5 years study

Introduction: Thyroid fine-needle aspiration cytology (FNAC) has gained significance as a quick, safe, and relatively simple method to differentiate malignant from benign thyroid nodules and is regarded as the gold-standard first-line diagnostic test in the evaluation of thyroid nodules. The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) established a standardized, category-based reporting system for thyroid FNAC with each category having an implied cancer risk. However, the optimal management of thyroid nodules in the Bethesda III and IV categories is controversial, given the variable malignancy rates. Aims/Objectives: (1) Analysis of the cytomorphological characteristics of patients with categories III and IV of “TBSRTC.” (2) Assessment of risk of malignancy of TBSRTC category III, IV, and substratification of TBSRTC category III. Materials and Methods: A retrospective and prospective study of cases categorized under TBSRTC as category III and IV at a tertiary-care center. Cytological along with their histological results were compared. Results: We identified an overall malignancy rate of 33% for nodules belonging to Bethesda category III and a malignancy rate between 19% and 33% for Bethesda category IV. Also, a significantly higher risk of malignancy in subcategories with nuclear and architectural atypia (66.6%) than only architectural atypia (28.7%). Conclusion: Although surgery is recommended in most of these cases, cytomorphology helps to predict the final histopathological findings with greater accuracy. Substratification of category III into subgroups may help reduce the heterogeneity of the atypia of undetermined significance/follicular lesion of undetermined significance category and more.