Does the Diagnostic Performance of the Pathologist on the Indeterminate Categories of the Bethesda System for Reporting Thyroid Cytopathology Vary between Pediatric and Adult Patients?

Introduction: The objectives of this study were to investigate the variation in the use of indeterminate categories of The Bethesda System for reporting thyroid cytopathology across age groups, particularly focusing on atypia of undetermined significance (AUS) category, and discern the potential role of a bias in pathologist's interpretation when dealing with pediatric patients.

Materials and methods: To highlight a more refined diagnostic pattern, thyroid fine-needle aspirations reported by a single pathologist over a span of 10 years enrolled to the study. A total of 8,827 cases from patients aged between 2 and 89 were categorized for each decades of ages. For the AUS category, AUS to malignant (AUS:M) ratio was calculated, and variations in distinct age groups and across the years were noted.

Results: The rate of indeterminate categories was 19% for the pediatric cases and 11% for the adults. When compared to adults, AUS diagnosis was more common in pediatric patients (14% vs. 9%), with rates of malignancy (ROMs) 54% and 45%, respectively. The AUS:M ratio during the study period ranged between 0.5 and 2.3 (mean 1.4). AUS:M ratio was highest in children below the age 11. Among AUS subtypes, AUS-nuclear predominated in both age groups, and papillary thyroid carcinoma emerged as the most common malignancy after resection. Follicular neoplasia category was higher in pediatric patients than in adults (4% vs. 1%), with similar ROMs (29% vs. 32%).

Conclusion: Indeterminate cytology diagnosis and subsequent ROM is higher in pediatric patients, which might be attributable to a slightly higher use of AUS diagnosis in the youngest children.