Fluorodeoxyglucose uptake in absence of CT abnormality on PET-CT: What is it?

Figure 5 Colonic uptake abutting the margin of the liver. A 59-year-old man with newly diagnosed pancreatic cancer had fluorodeoxyglucose positron emission tomography-computer tomography (PET-CT) for staging. Axial PET image of the upper abdomen shows a small focus of increased uptake abutting the anterior margin of the liver (arrow). But there is no visible hepatic lesion on the integrated CT. A magnetic resonance imaging was also negative for any lesion in the liver. The uptake is from the adjacent transverse colon with slight motion artifact and mis-registration of PET and CT images.