Sonographic risk stratification of FDG-avid thyroid nodules using the Thyroid Imaging Reporting and Data System

Area of Science:

• Nuclear medicine
• Radiology
• Endocrinology

Background:

• Positron emission tomography/computed tomography (PET/CT) scans increasingly detect incidental thyroid nodules.
• 2-[18F]-fluoro-2-deoxy-d-glucose (FDG)-avid nodules carry a high risk of malignancy and require further investigation.
• Limited research exists on risk stratification for FDG-avid thyroid incidentalomas.

Purpose of the Study:

• To evaluate the efficacy of the American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TIRADS) classification in risk stratification.
• To assess the need for fine-needle aspirate cytology (FNA) in incidentally detected FDG-avid thyroid nodules.

Main Methods:

• Retrospective data collection of FDG-avid thyroid incidentalomas over 10 years.
• Nodules characterized using ACR TIRADS classification.
• Fine-needle aspirate cytology (FNAC) performed, with results classified using the Bethesda system (excluding non-diagnostic samples).

Main Results:

• Malignancy rates were 36% for low-risk and 45% for high-risk nodules (P=0.516).
• ACR TIRADS sensitivity and specificity for malignancy detection were 56% and 54%, respectively.
• No malignant nodules were found in TIRADS 1 or 2 categories; absence of suspicious sonographic features had a 1.0 negative predictive value.

Conclusions:

• FDG-avid nodules classified as TIRADS 1 or 2, or those lacking suspicious ultrasound features, have a 0% incidence of malignancy and may not require FNA.
• FDG-avid nodules classified as TIRADS 3 or higher warrant FNA due to high malignancy risk and the TIRADS system's limited sensitivity.