Evaluation of selected ultrasound features of thyroid nodules with atypia of undetermined significance/follicular lesion of undetermined significance for the Bethesda reporting system for thyroid cytology.

Background and objective: The risk of malignancy from "atypia of undetermined significance/follicular lesion of undetermined significance" (AUS/FLUS) is estimated to lie between 5% and 15%; however, some authors suggest that the risk of malignancy in AUS/FLUS depends upon specific clinical situations. This was a retrospective study which aimed to determine the incidence and risk of thyroid cancer (TC) based upon selected ultrasound features from patients with thyroid nodules (TN) classified as AUS/FLUS.

Methods: Univariate and multivariate logistic regression analyses were used to identify significant associations between ultrasound features and the risk of TC.

Results: Of 127 patients with TN classified as AUS/FLUS who underwent thyroidectomy, 114 (89.8%) had benign disease while 13 (10.2%) had TC. Univariate analysis identified several significant predictors for TC (all p <0.05), including microcalcifications, hypoechogenicity, the prevalence of irregular margins, a taller rather than a wide form, high vascularity, and fast tumor growth. Multivariate analysis further showed that microcalcifications (odds ratio =21.37; p =0.024) and fast growth (odds ratio =22.70; p =0.021) were significant and independent factors associated with the risk of developing TC.

Conclusion: Microcalcifications and fast growth of the TN could therefore be used as predictive factors for the development of TC in patients with AUS/FLUS.