Abstract

18F-FDG PET/CT is widely used in oncology for staging, restaging, and for treatment response assessment. Beyond its oncologic applications, FDG’s non-specific uptake can reveal previously unsuspected inflammatory, infectious, or benign conditions –incidentalomas- which may influence diagnostic interpretation and clinical decision-making. Recognizing these findings is particularly important for young or less-experienced nuclear medicine physicians.

In this case series, we report a number of non-malignant incidental findings rarely or never documented on PET/CT imaging. For this, we retrospectively reviewed 753 FDG PET/CT examinations performed over one-year period on a digital PET/CT system. All patients underwent standardized imaging protocols, including fasting, glucose level control, 18F-FDG injection (3MBq/kg), and low-dose computed tomography for attenuation correction and lesion characterization. PET/CT studies were independently interpreted by two senior nuclear medicine physicians in correlation with clinical history, with a third opinion required in case of discrepancy.

A total of 169 cases included incidental findings unrelated to the primitive malignancy (22%), mostly including common benign and clinically insignificant findings such as degenerative, dental, muscular and thyroid related unspecific uptake. Only five representative and clinically relevant incidental findings were selected to be reported in our paper: Lipomatous hypertrophy of the interatrial septum mimicking cardiac metastasis, a fatal acute coronary sinus thrombosis; a masked acute appendicitis, a rare U-inverted pelvic horseshoe kidney; and finally a functioning pituitary microadenoma initially suspected of paraneoplastic hyperprolactinemia. These cases illustrate the broad spectrum of clinically significant incidental findings detectable on oncologic 18F-FDG PET/CT. Awareness of atypical patterns of physiological, benign, and inflammatory FDG uptake is essential to avoid misinterpretation, guide appropriate management, and improve diagnostic confidence.