Ultrasound Risk Stratification Systems and SUVmax in PET-Positive Thyroid Incidentalomas: Competing or Complementary Tools?

Dear Editor,

We read with great interest the article by Kostek et al^[1] evaluating whether ultrasonographic assessment or FDG uptake should guide fine-needle aspiration biopsy (FNAB) decisions in thyroid incidentalomas detected on ^18F-fluorodeoxyglucose positron emission tomography/computed tomography (^18F-FDG PET/CT). We also noted the subsequent correspondence by Vatankulu and Sager, who questioned the diagnostic utility of SUVmax in thyroid incidentalomas. Both publications address an important and ongoing debate regarding the optimal management of PET-positive thyroid incidentalomas.^[2]

In their study, Kostek et al.^[1] reported that an SUVmax cutoff value of 5.5 predicted malignancy with a sensitivity of 71.4% and a specificity of 68.6%, leading the authors to suggest that FNAB should be planned for nodules with SUVmax values above this threshold. In contrast, Vatankulu and Sager emphasized the potential influence of selection bias and argued that SUVmax alone has limited value for predicting thyroid malignancy, advocating greater reliance on ultrasonographic evaluation.^[2]

We believe that the available evidence supports a more balanced interpretation. In our recently published study, which included 236 cytologically or histopathologically verified PET-positive thyroid incidentalomas, malignant nodules demonstrated significantly higher SUVmax values than benign nodules, and receiver operating characteristic analysis identified an optimal SUVmax cutoff value of 5.67 for malignancy prediction.^[3] The remarkable similarity between this threshold and the value reported by Kostek et al.^[1] suggests that increased FDG uptake is not merely an incidental finding and may provide clinically relevant information regarding malignancy risk.

However, our findings also demonstrated that ultrasound-based risk stratification systems (US-RSSs) outperformed SUVmax alone.^[3] The areas under the curve were 0.901 for EU-TIRADS, 0.895 for K-TIRADS, and 0.877 for ACR-TIRADS, whereas the corresponding value for SUVmax was 0.771.^[3] Furthermore, an EU-TIRADS score ≥4 achieved a sensitivity of 94.7% and a specificity of 78.3%, compared with 68.4% and 69.7%, respectively, for SUVmax >5.67.^[3] These findings indicate that ultrasonographic risk stratification provides greater discriminatory power for malignancy prediction than metabolic activity alone.

Another important consideration is the inherent limitation of retrospective studies evaluating thyroid incidentalomas in patients undergoing PET/CT for non-thyroid malignancies. As acknowledged by Kostek et al.,^[1] a substantial proportion of patients could not complete the diagnostic workup because of advanced disease, ongoing oncological treatment, loss to follow-up, or refusal of further investigations. Consequently, histopathological confirmation is often available only in a selected subgroup of patients, which may influence the estimated diagnostic performance of imaging parameters. Similar limitations have affected most studies in this field and continue to represent a challenge when interpreting the true predictive value of SUVmax.

Nevertheless, we respectfully suggest that completely dismissing the clinical value of SUVmax may also oversimplify the available evidence. The consistency between the SUVmax thresholds identified in our study and that reported by Kostek et al.,^[1] together with the significantly higher SUVmax values observed in malignant nodules, supports the notion that metabolic activity contributes meaningful information to risk assessment.^[3] Rather than functioning as a standalone diagnostic marker, SUVmax may be most useful when interpreted alongside established ultrasonographic risk stratification systems.

Taken together, the findings of Kostek et al.,^[1] the concerns raised by Vatankulu and Sager, and the results of our study suggest that FDG uptake and ultrasound-based risk stratification should not be viewed as competing approaches.^[1–3] Instead, they appear to provide complementary information regarding malignancy risk in PET-positive thyroid incidentalomas. While increased FDG uptake may heighten clinical suspicion, ultrasound-based risk stratification—particularly EU-TIRADS—seems to offer superior performance for selecting patients who may benefit from FNAB. Future prospective multicenter studies incorporating standardized cytological or histopathological verification and integrated risk models combining metabolic and ultrasonographic parameters may help establish more accurate and clinically applicable management strategies.

We congratulate the authors on their valuable contribution to this evolving field and believe that continued investigation will further refine the diagnostic approach to thyroid incidentalomas detected on ^18F-FDG PET/CT.

Conflict of Interest

The author declare that there is no conflict of interest.

Financial Disclosure

This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Use of AI for Writing Assistance

Declaration of AI-Assisted Technology Artificial intelligence-assisted technology (ChatGPT, OpenAI) was used solely to improve language expression, manuscript organization, and editorial drafting during manuscript preparation. The author critically reviewed, revised, and approved all content and takes full responsibility for the accuracy, integrity, and originality of the manuscript. No AI-assisted technology was used for data collection, data analysis, interpretation of results, or generation of scientific conclusions.