Asymmetric 18F-FDG Uptake in the Infradiaphragmatic Brown Adipose Tissue (BAT) Mimicking Adrenal Metastasis: A Relatively Rare Site of Brown Fat and a Potential Source for False Positive FDG-PET Study.

FDG uptake in the metabolically active brown adipose tissue (BAT) is a source of significant concern while interpreting FDG-PET studies. It is also of great interest due to its potential implications for obesity research. In this communication, we describe hitherto unreported asymmetric BAT uptake in the abdomen, persisting after diazepam intervention in the repeat PET study on a separate day. The patient did not have any evidence of disease even at 24 months' follow up. The present case is a useful addition to the current body of literature of false positive FDG-PET due to BAT uptake in unusual location and underscores the importance of high index of suspicion and careful correlation, whenever one comes across an unusual PET finding in a given clinical situation. This assumes important diagnostic value particularly when it coexists in the setting of malignancy where the disease can be falsely upstaged by misinterpretation. The literature relevant to the report is discussed and a schema is suggested for correct interpretation.