Definitions of Incidental [18F]FDG PET/CT Findings in the Literature: A Systematic Review and Definition Proposal

Objectives: The objectives of this study were (1) to systematically review the currently used definitions of incidental 2-deoxy-2-[F-18]fluoro-D-glucose positron emission tomography/computed tomography findings (IPFs) in the literature and (2) to propose an IPF definition. Methods: A systematic search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The search was guided by the question "How is IPF defined?" and was performed in MEDLINE, Embase, and the Cochrane Library. The retrieved studies were reviewed and analyzed. The definitions of IPFs in the included studies were compiled into two sets of categories based on the description of FDG uptake and the specification of clinical factors in defining IPFs. Results: The systematic literature search identified 4852 publications accessible for title-abstract screening, which yielded 395 studies for full-text assessment. Sixty-five studies met the eligibility criteria and were included. Sixty-two percent mentioned "FDG uptake" in their definition. In 40% of the definitions, "Focal FDG uptake" was specified, while "FDG uptake in the surrounding tissue" was included in 15%. Fifty-seven percent stated that IPFs were "Unrelated to PET/CT indication". Thirty-four percent specified IPFs as "Present in other organ than PET/CT indication", whereas 20% included "No known disease related to IPF". Seventeen percent of the definitions comprised a "New finding", while 15% and 11% encompassed a "Clinical asymptomatic patient" and "Not a metastasis", respectively. Finally, 5% of the definitions included "Potential clinical significance". Conclusions: No generally accepted definition of IPFs currently exists. We propose an IPF definition based on explicit FDG uptake and clinical patient-related factors.