FDG uptake in brown adipose tissue mimicking an adrenal metastasis: source of false-positive interpretation.

Brown adipose tissue (BAT) uptake of F-18 fluorodeoxyglucose (FDG) poses a significant challenge to positron emission tomography interpretation. BAT is not only localized to the supraclavicular areas, but is also seen in the neck, mediastinum, axillae, costovertebral junctions, and retrocrural and periadrenal regions. We illustrate a case of typical supraclavicular BAT uptake in association with a discrete right adrenal region focus. On repeat study after diazepam administration, both the supraclavicular and periadrenal uptake were abolished. BAT uptake is an important cause of false-positives; when typical supraclavicular BAT uptake is seen, abnormalities in other areas of BAT distribution should be viewed with caution.