Unexpected focal fluorodeoxyglucose uptake in main organs; pass through or pass by?

Abstract

Since the inception of fluorine-18 fluorodeoxyglucose (F-18 FDG), positron emission tomography/computed tomography (PET/CT) utilizing F-18 FDG has become widely accepted as a valuable imaging modality in the field of oncology, with global prevalence in clinical practice. Given that a single Torso PET/CT scan encompasses the anatomical region from the skull base to the upper thigh, the detection of incidental abnormal focal hypermetabolism in areas of limited clinical interest is both feasible and not uncommon. Numerous investigations have been undertaken to delineate the distinctive features of these findings, yet the outcomes have proven inconclusive. The incongruent results of these studies present a challenge for physicians, leaving them uncertain about the appropriate course of action. This article provides a succinct overview of the characteristics of fluorodeoxyglucose, followed by a comprehensive discussion of the imaging findings and clinical significance associated with incidental focal abnormal F-18 FDG activity in several representative organs. In conclusion, while the prevalence of unrecognized malignancy varies across organs, malignancies account for a substantial proportion, ranging from approximately one-third to over half, of incidental focal uptake. In light of these rates, physicians are urged to exercise vigilance in not disregarding unexpected uptake, facilitating more assured clinical decisions, and advocating for further active evaluation.

Keywords: Incidental; Focal; Incidentaloma; Fluorodeoxyglucose; Positron emission tomography; Hypermetabolism

Core Tip: Unexpected incidental focal fluorine-18 fluorodeoxyglucose uptake on positron emission tomography/computed tomography is not an uncommon finding. The nature of this uptake has been the subject of various studies, with outcomes varying depending on the organ in which it manifests. A noteworthy finding from these investigations reveals that over one-third of such uptakes were determined to be malignant. This observation underscores the importance of conducting further examinations in cases where incidental uptake is identified, as it could potentially serve as a crucial indicator for malignancy.