Diagnostic performances of five US risk stratification systems for malignancy in focal [18F]FDG-PET/CT thyroid incidentalomas

Abstract

Objectives: This study assessed the risk of malignancy (ROM) of nodules classified by five US risk stratification systems (US-RSSs) and evaluated the diagnostic performances of US-RSSs with biopsy criteria for diagnosing malignancy in focal [¹⁸F]fluorodeoxyglucose (FDG)-PET/CT thyroid incidentalomas (TIs).

Materials and methods: This retrospective cohort study included 216 patients with 236 [¹⁸F]FDG-PET/CT TIs, of whom 208 (96.3%) were oncology patients. The primary outcome included the diagnostic performances of five US-RSSs with biopsy criteria for diagnosing malignant tumors. Secondary outcomes included the ROM of nodules classified by US-RSSs and the diagnostic performance of US-RSS criteria combined with maximum standardized uptake value (SUVmax).

Results: The malignancy risk of intermediate-risk TIs was higher (33.8-48.2%) than the suggested ROM across all RSSs (p < 0.01). Low-risk category TIs had a significantly higher ROM (> 20%) only in Chinese-Thyroid Imaging Reporting and Data System (C-TIRADS; 35.0%, p < 0.01). The sensitivity for overall and aggressive malignancies was highest (97.3% and 100%, respectively) in the American Thyroid Association system and Korean-TIRADS, but lower (86.7-90.7% and 80.0-86.7%, respectively) in other RSSs for 189 TIs > 1 cm. American College of Radiology (ACR)-TIRADS showed the highest specificity (50.0%) and lowest unnecessary biopsy rate (30.2%, p < 0.01). Combined SUVmax-US-RSS criteria demonstrated increased sensitivity in ACR-TIRADS (96.0%, p = 0.02), but also showed greater unnecessary biopsy rates (p < 0.01).

Conclusion: Intermediate-risk TIs had greater ROM across RSSs, while low-risk TIs showed a significant increase only in C-TIRADS. Although US-RSSs can reduce unnecessary biopsies, European-TIRADS, ACR-TIRADS, and C-TIRADS demonstrated relatively lower sensitivity for aggressive malignancies.

Key points: Question The diagnostic performance of US risk stratification systems (US-RSS) from various professional societies remains unestablished in the assessment of focal [¹⁸F]fluorodeoxyglucose (FDG)-PET/CT thyroid incidentalomas. Findings While US-RSSs reduce unnecessary biopsies, European-, American College of Radiology-, and Chinese-thyroid imaging reporting and data systems (TIRADS) demonstrated relatively lower sensitivity for aggressive malignancies. Clinical relevance US-RSSs stratify malignancy risk in focal [¹⁸F]FDG-PET/CT incidentalomas, but lower biopsy size cutoffs may be needed for intermediate-risk nodules in European- and American College of Radiology-TIRADS and low-risk nodules in Chinese-TIRADS, based on oncology patients' clinical context.

Keywords: Diagnosis; Incidentaloma; Positron emission tomography-computed tomography; Thyroid; Ultrasonography.