Pictorial Essay Review of Malignancies with Low FDG-Avidity on PET/CT

18Fluorodeoxyglucose-Positron Emission Tomography (18FDG-PET) is a medical imaging technique which utilizes 18FDG as a radiotracer to map out differences in cell function and metabolic activity for oncologic detection. One of the drawbacks of 18FDG PET is that the 18FDG radioisotope does not demonstrate avid uptake among every cancer type, and there are recognized factors deriving from both patients and tumors which elicit this phenomenon. We will discuss the factors that affect 18FDG avidity, show various malignancies that typically present with low 18FDG avidity, explain attributable factors causing low avidity and propose alternative imaging modalities. This pictorial essay aims to provide a reference for different malignancies whose detection may potentially be missed or underdiagnosed with 18FDG PET/CT.