Histopathological Outcomes of Thy3 Thyroid Nodules: Malignancy Risk in an Indeterminate Cytology Cohort

Introduction: In our centre, we observed a higher than nationally reported malignancy rate among indeterminate thyroid nodules. As a result, we adopted a practice of offering diagnostic hemithyroidectomy to patients with Thy3a cytology. This study aims to evaluate the malignancy rate of indeterminate thyroid nodules following this change in practice. Methods: We conducted a retrospective study of patients with Thy3 thyroid nodules who underwent thyroidectomy at our centre between January 2022 and December 2023. We recorded and analysed patients’ demographics, nodule size, and histopathological outcomes. Results: During the study period, 262 thyroidectomies were performed, of which 136 (51.9%) had a pre-operative Thy3 cytology. The majority of patients were females (N=97, 71.3%), and the average age was 51.4 years. The overall malignancy rate was 24.3%. In the Thy3a group (N=109), the malignancy rate was 19.3%, and the nodule size in the benign group was larger (38.1mm versus 31.7mm). In the Thy3f group (N=27), the malignancy rate was 44.4%, and the nodule size did not differ significantly between the groups (24.7mm versus 25.2mm). Conclusion: Almost every second patient with Thy3f cytology and approximately one in five patients with Thy3a cytology were diagnosed with thyroid cancer. Given the significant variation between centres, we recommend that individual endocrine units assess their local malignancy rates to better inform discussions with patients.