Rates of Malignancy in Cytology Indeterminate Thyroid Nodules: A Single Center Surgical Series

Background: Due to the high variability in malignancy rate among cytologically indeterminate thyroid nodules (Bethesda categories lll-V), the American Thyroid Association recommends that each center define its own categorical cancer risk. Objectives: To assess cancer risk in patients with cytologically indeterminate thyroid nodules who were operated at our center. Methods: In a retrospective study, we analyzed the pathology results of all the patients whose fine needle aspiration results showed Bethesda lll-V cytology and who subsequently underwent total thyroidectomy or lobectomy from December 2013 to September 2017. Results: We analyzed 56 patients with indeterminate cytology on fine needle aspiration. Twenty-nine (52%) were defined as Bethesda III, 19 (34%) Bethesda IV, and 8 (14%) Bethesda V category. Malignancy rates were 38%, 58%, and 100% for Bethesda categories III, IV, and V, respectively. Most malignancies in Bethesda categories III and IV were follicular in origin (follicular thyroid carcinoma and follicular type papillary thyroid carcinoma), while 100% of the patients with Bethesda category V were diagnosed with classical papillary thyroid carcinoma. No correlation was found between sonographic and cytological criteria of nodules with Bethesda categories III and IV and rates of malignancy. Conclusions: We found higher than expected rates of malignancy in indeterminate cytology. This finding reinforces the guidelines of the American Thyroid Association to establish local malignancy rates for thyroid nodules with indetermined cytology.