Solution: Brown fat is a potential source for a false positive FDG-PET scan. Approximately 2% of patients will have this kind of FDG uptake and it is much more common in children than in adults and more common in women than in men. The SUV can be quite high, mean of 5.7 in one study, so that does not help in discrimination. However, the distribution is often quite typical and symmetric. Knowledge of this potential pitfall is critical to prevent misinterpretation of this finding as malignancy. PET/CT is obviously helpful since you will note on the correlation that the increased uptake is in fat, not in soft tissue.