Malignant risk of pediatric Bethesda category III thyroid nodules subcategorized by nuclear atypia and other: A single institution experience.

BACKGROUND: The 2023 Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) divides AUS diagnoses into two major subcategories: atypia of undetermined significance (AUS) nuclear atypia (AUS-N) and other (AUS-O). This study aims to compare the histological outcome and malignant rate of pediatric AUS thyroid nodules classified into AUS-N and AUS-O subcategories.

DESIGN: A search of our institutional electronic pathology database for the period from January 2012 to July 2023 was conducted to identify pediatric (<21 years old) thyroid nodules that were interpreted as AUS and subsequently had surgery. Cases were further divided into AUS-N and AUS-O subcategories. Results of follow-up surgical resections were collected. The malignant rate was calculated and compared between AUS-N and AUS-O groups.

RESULTS: The study identified 62 thyroid nodules from 58 pediatric patients. Among these nodules, 29 and 33 were subcategorized as AUS-N and AUS-O, respectively. Both groups exhibited a female predominance and displayed a similar nodule size distribution. Histological analysis revealed 15 carcinomas in AUS-N nodules, including 11 cases of classic papillary thyroid carcinoma (PTC) and four cases of follicular type of PTC. In contrast, in the AUS-O group, a total of five carcinomas were documented, including two PTCs and three oncocytic thyroid carcinomas. Notably, the malignant rate of AUS-N nodules (52%) is significantly higher than that of AUS-O nodules (15%) (p = .002).

CONCLUSION: In pediatric AUS thyroid nodules, the malignant risk in AUS-N is significantly higher than that in AUS-O. These findings may guide more appropriate clinical triage and/or improve management of pediatric patients with AUS thyroid nodules.