Clinical significance of suspicious incidental FDG uptake: a comparison between digital PET/CT and conventional...

To compare the clinical significance of incidental ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake detected on silicon photomultiplier-based digital positron emission tomography/computed tomography (dPET) versus conventional positron emission tomography/computed tomography (cPET), focus on suspicious incidental lesions and incidental malignancies.

This retrospective single-center study included patients who underwent cPET from April 2019 to March 2020 and dPET from June 2020 to May 2021. Epilepsy PET and cardiac PET examinations requiring prolonged fasting protocols were excluded. Suspicious incidental FDG uptake was defined as a lesion unrelated to the primary indication or previously known disease, showing visually increased uptake and explicitly recommended for further evaluation in the original radiology report because malignancy was considered a concern. Lesions for which only follow-up was advised were excluded. Organ-specific analyses were performed exploratorily. Detection rates, organ distribution, malignant outcomes, and maximum standardized uptake value (SUVmax) were compared between groups.

A total of 1,815 cPET examinations and 1,769 dPET examinations were analyzed. Suspicious incidental FDG uptake was identified more often with dPET than with cPET (149/1,769 [8.4%] vs 97/1,815 [5.3%], p < 0.01). Further diagnostic evaluation was performed in 73 cPET lesions and 111 dPET lesions, and confirmed incidental malignancy was identified in 15 and 29 lesions, respectively, corresponding to 0.83% (95% CI: 0.50-1.36%) and 1.64% (95% CI: 1.15-2.35%) of all examinations (p < 0.05). Colorectal cancer was the most common incidental malignancy in both groups. Prostate cancer was the second most frequent incidental malignancy in the dPET/CT group but was not confirmed in the cPET/CT group. Median SUVmax of incidental lesions was higher with dPET than with cPET (6.8 [4.8-9.7] vs 5.5 [4.2-9.0], p < 0.05). However, SUVmax did not significantly distinguish malignant from non-malignant lesions in either group.

In routine clinical practice, implementation of dPET was associated with increased detection of suspicious incidental FDG uptake and confirmed incidental malignancy compared with cPET. This difference was most apparent for colorectal and prostatic lesions. However, SUVmax alone had limited value for distinguishing malignant from non-malignant incidental lesions, indicating that organ-specific clinical interpretation remains essential.