Unrecognized renal transplants as a potential source of false-positive interpretation of FDG PET.

Renal transplantation has become an effective therapy for patients with late-stage renal disease. Fluorodeoxyglucose (FDG) positron emission tomography (PET) is accepted as an important diagnostic technique in the evaluation of suspected or known malignancies or other disorders in the day-to-day practice of medicine. Because FDG is excreted from the kidneys into the urine, unrecognized renal transplants can appear as malignant lesions. Familiarity with the clinical history is a prerequisite in the correct interpretation of FDG PET images in this setting. In addition, FDG PET images should be correlated with anatomic images when such studies are available. When neither clinical history nor anatomic images are available, a combination of "abnormal" activity in the pelvis and absence of normal renal activity should raise suspicion of the existence of a renal transplant.