The prevalence and surgical outcomes of Hürthle cell lesions in FNAs of the thyroid: A multi-institutional study in 6 Asian countries

Background: Hürthle cell-rich nodules (HCNs) encompass non-neoplastic to malignant lesions. There is paucity of literature on the frequency distribution of HCNs among Bethesda categories, histologic follow-up, risk of malignancy (ROM), and risk of neoplasia (RON). The objective of this retrospective, multi-institutional study was to determine the prevalence of the cytologic diagnostic category and surgical outcomes of patients with HCN. Methods: Nine tertiary health centers representing 6 Asian countries participated. Cases were retrieved from respective databases. The Bethesda System for Reporting Thyroid Cytopathology was used. Cytology results were correlated with surgical diagnoses. Results: Of 42,190 thyroid aspirates retrieved, 760 (1.8%) had a Hürthle cell predominance. Most (61%) were categorized as atypia of undetermined significance/follicular lesion of undetermined significance, Hürthle cell type” (AUS-H); 35% were categorized as follicular neoplasm, Hürthle cell type (FN-H); and 4% were categorized as suspicious for malignancy (SFM). Histologic follow-up was available for 288 aspirates (38%). Most were benign on resection (66%), and the most common histologic diagnosis was Hürthle cell adenoma (28.5%). The ROM for AUS-H, FN-H, and SFM, as calculated on resected nodules, was 32%, 31%, and 71%, respectively; and the RON was 47%, 81%, and 77%, respectively. The 5 institutions that had an AUS-H:HCN ratio below 0.5 diagnosed HCN less frequently as AUS-H than as FN-H. Conclusions: This is the largest, contemporary, multi-institutional series of HCNs with surgical follow-up. Although there was wide interinstitutional variation in prevalence and surgical outcomes, there was no significant difference in the ROM among institutions. The categories AUS-H and FN-H had a similar ROM for resected nodules.