The contribution of PET/MRI in benign/malignant nodule separation in thyroid incidentalomas detected in FDG PET/CT imaging

Abstract

Introduction and objectives

Incidentalomas of the thyroid gland are frequently observed in oncological patients undergoing FDG PET/CT imaging for staging or treatment response assessment. This study aims to investigate the utility of SUVmax and ADC values measured by PET/MRI in distinguishing between benign and malignant thyroid nodules.

Materials and methods

We selected 108 patients (72 females, 36 males; mean age 54 ± 12 years) who underwent routine oncological FDG PET/CT scans for staging or treatment response assessment, with nodule sizes greater than 1 cm. A one-bed neck PET/MRI scan followed the whole-body PET/CT. SUVmax values were measured, and ADC maps were created using DWI with b factors of 50 and 1000 s/mm². SUVmax and ADC values were correlated with FNAC results.

Results

FNAC results revealed 76 (70.4%) benign and 32 (29.6%) malignant nodules among the 108 patients. The mean SUVmax of malignant nodules was significantly higher than that of benign nodules (10.6 ± 8.3 vs. 5.94 ± 5.2, p < 0.001). Similarly, the mean ADC value was lower in malignant nodules compared to benign ones (1.4 ± 0.6 × 10⁻³ mm²/s vs. 1.8 ± 0.4 × 10⁻³ mm²/s; p < 0.001). A significant but weak correlation was found between FNAC results and mean SUVmax (r = 0.335), as well as a significant weak negative correlation with mean ADC values (r = −0.355). Using a cut-off value of 6 for SUVmax and 1.56 × 10⁻³ mm²/s for ADC, the sensitivity, specificity, and accuracy for SUVmax were 68.7%, 73.6%, and 72.1%, respectively, while for ADC, they were 71.8%, 69.7%, and 70.4%, respectively. The PET/MRI system demonstrated a relative sensitivity, specificity, accuracy, PPV, and NPV of 90.62%, 51.32%, 62.96%, 43.94%, and 92.86%.

Conclusion

This study is one of the first in the literature to explore the use of FDG PET/MRI, a single-stop device, in distinguishing between benign and malignant thyroid nodules with high sensitivity and NPV.