Beyond the Primary Tumor: Malignancy Risk and Evaluation Strategies for ¹⁸F-FDG PET/CT-Detected Incidentalomas

The increasing use of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) imaging has led to the frequent detection of incidentalomas. This study aimed to investigate the prevalence, locations, malignancy rates, and clinical evaluations of incidentalomas detected during preoperative staging with ¹⁸F-FDG PET/CT in patients with surgically relevant primary tumors.

A total of 251 patients who underwent preoperative ¹⁸F-FDG PET/CT imaging between January 2019 and December 2023 were retrospectively analyzed. Incidental uptake sites were classified into six anatomical regions: thyroid, colon, rectum, prostate, cervix/uterus, and breast. Data regarding maximum standardized uptake value (SUV_max) values, biopsy status, imaging follow-up, and histopathological outcomes were recorded and compared with population-based incidence data from the literature.

The most frequent incidentalomas were detected in the thyroid (11.6%), followed by cervix/uterus (9.6%), colon (7.6%), prostate (4.4%), breast (2.4%), and rectum (2.0%). Malignancy was confirmed in incidentalomas of the thyroid (85.7%), prostate (83.3%), colon (71.4%), rectum (50.0%), and breast (33.3%). Malignancy rates for the thyroid, breast, colorectal, and prostate groups were significantly higher than population-based estimates (p<0.05). No statistically significant correlation was found between SUV_max and malignancy status across localization groups.

Incidental findings on ¹⁸F-FDG PET/CT imaging are common and carry a considerable risk of malignancy, particularly in thyroid, prostate, and colorectal sites. Given the observed diagnostic yield, further clinical evaluation, including tissue diagnosis, should be considered in cases with focal uptake, especially when located in high-risk anatomical regions. Awareness of these findings is essential for timely management and appropriate therapeutic decision-making.