Pitfalls in oncologic diagnosis with FDG PET imaging: Physiologic and benign variants

A rapidly emerging clinical application of positron emission tomography (PE T) is the detection and staging of cancer with the glucose analogue tracer 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG). Proper interpretation of FDG PET images requires knowledge of the normal physiologic distribution of th e tracer, frequently encountered physiologic variants, and benign pathologi c causes of FDG uptake that can be confused with a malignant neoplasm. One hour after intravenous administration, high FDG activity is present in the brain, the myocardium, and-due to the excretory route-the urinary tract. El sewhere, tracer activity is typically low, a fact that allows sensitive dem onstration of tracer accumulation in many malignant neoplasms. Interpretive pitfalls commonly encountered on FDG PET images of the body obtained 1 hou r after tracer administration can be mistaken for cancer. Such pitfalls inc lude variable physiologic FDG uptake in the digestive tract, thyroid gland, skeletal muscle, myocardium, bone marrow, and genitourinary tract and beni gn pathologic FDG uptake in healing bone, lymph nodes, joints, sites of inf ection, and cases of regional response to infection and aseptic inflammator y response. In many instances, these physiologic variants and benign pathol ogic causes of FDG uptake can be specifically recognized and properly categ orized; in other instances, such as the lymph node response to inflammation or infection, focal FDG uptake is nonspecific.