Approach to Bethesda system category III thyroid nodules according to US-risk stratification

Area of Science:

• Endocrinology
• Oncology
• Radiology

Background:

• Bethesda category III (atypia of undetermined significance/follicular lesion of undetermined significance) thyroid nodules pose management challenges.
• Distinguishing benign from malignant nodules in this category is crucial to avoid overtreatment.

Purpose of the Study:

• To evaluate the utility of the Korean Thyroid Imaging Reporting and Data System (K-TIRADS) in managing Bethesda III thyroid nodules.
• To assess the malignancy risk associated with different K-TIRADS categories within Bethesda III nodules.
• To determine if K-TIRADS can guide decisions on repeat examination versus surgery.

Main Methods:

• Retrospective analysis of 161 Bethesda III thyroid nodules undergoing surgery (2016-2019).
• Repeat examinations using ultrasonography-guided fine-needle aspiration (US-FNA) or core needle biopsy (CNB) were performed.
• K-TIRADS categories were assigned to all nodules, and malignancy proportions were correlated with K-TIRADS and Bethesda subcategories (AUS/FLUS).

Main Results:

• Malignancy rates in Bethesda III nodules significantly increased with K-TIRADS suspicion levels (low: 60.0%, intermediate: 88.2%, high: 100%).
• A significant difference in malignancy proportion was observed between atypia of undetermined significance (AUS) and follicular lesion of undetermined significance (FLUS) (94.2% vs. 40.0%).
• Conclusive results from repeat biopsies were higher for intermediate (83.3%) and high (88.8%) suspicion K-TIRADS nodules compared to low suspicion (58.3%).

Conclusions:

• K-TIRADS stratification aids in managing Bethesda III thyroid nodules, particularly for predicting papillary carcinoma.
• Low suspicion K-TIRADS nodules within Bethesda III require careful risk-benefit assessment before surgery or repeat biopsy.
• K-TIRADS is less effective in predicting follicular carcinoma within the Bethesda III category.