Physiological and Normal Variations in FDG uptake: A pictorial review.

Objectives: 18-F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) scan, now considered the cornerstone of oncologic imaging requires knowledge of the normal patterns and variations in FDG distribution in the whole body. We aim to evaluate organ wise spectrum of distribution patterns, intensities and variations in normal physiological FDG uptake routinely encountered on a daily basis.

Methods: We retrospectively reviewed all the oncologic PET CT cases over a2-year period and collected the most illustrative cases demonstrating the wide spectrum of physiologic and normal variations in FDG uptake.

Results: A pictorial review of organ wise spectrum of distribution patterns, intensities and variations in normal physiological FDG uptake is presented. In each case the teaching points are separately highlighted

Conclusion: This pictorial review illustrates the physiological and normal variations in FDG uptake and will help in increasing the diagnostic accuracy of PET CT reports and thereby reducing the number of unnecessary follow-up studies/procedures. Research Support: Brain: greater uptake in the cerebral cortex, basal ganglia and thalami (grey matter), Variable uptake in the cord at C6-T1 and T12-L2 Head and Neck: wide spectrum of uptake pattern involving vocal cords, tonsils, waldeyer ring, parotid and submandibular glands. Thyroid: Focal and diffuse uptake patterns. Thymus: normal uptake in children, rebound thymic uptake Brown fat: various sites of symmetrical uptake in the neck, supraclavicular regions, axilla, mediastinum, retrocrural, suprarenal, perinephric and paravertebral regions. Skeletal muscle: Nonspecific uptake patterns in diaphragmatic crura, intercostal muscles, psoas muscles, paravertebral muscles, forearms, thenar and hypothenar muscles, muscles of mastication, enthesopathy. Myocardium: variable uptake pattern from absent to diffuse increased FDG activity(uptake in the atrial wall, ventricle wall, papillary muscle, atrial fibrillation, lipomatous hypertrophy of interatrial septum). Lungs: usually low uptake Mediastinum: Nonspecific hilar uptake Breast and Nipples: Mild uptake in young and post-menopausal women on hormone replacement therapy Aorta and Vessels: Nonspecific uptake Liver: heterogenous or patchy uptake Splenic: Normally less or similar uptake as Liver; but increased uptake Post GCSF treatment GI: variable activity involving esophagus, GE junction, stomach, pylorus, small and large bowel, patients on metformin GU: excreted activity; mild uptake in normal adrenal glands. Pelvic organ: Uptake in ovaries and endometrial canal (during menstruation).Mild uptake in the testis (more in young male). Bone marrow: Normally similar uptake as Liver but increased uptake Post GCSF treatment. Lymph node: Minimal uptake; increased uptake due to extravasation. Miscellaneous: various altered bio distribution patterns.