Concomitant Paravertebral FDG Uptake Helps Differentiate Supraclavicular and Suprarenal Brown Fat Uptake From Malignant Uptake When CT Coregistration Is Not Available

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Abstract
Objectives: Fluorine-18 fluorodeoxyglucose (F-18 FDG) uptake in brown adipose tissue (BAT) in the supraclavicular, superior mediastinal, paravertebral, and suprarenal/perinephric regions has been recognized. Of these 4 areas, uptake in the supraclavicular, mediastinal, and suprarenal areas may be difficult to differentiate from malignancy for those who interpret PET images only without CT coregistration or fusion. We assessed the prevalence and concomitance of F-18 FDG uptake in these 4 BAT regions. Methods: A total of 1495 F-18-FDG PET studies were reviewed. Distinct patterns compatible with BAT uptake in the 4 regions were graded and correlated with each other. Results: Of the 1495 studies, supraclavicular uptake was seen in 40 (2.7%), paravertebral uptake in 29 (1.9%), mediastinal uptake in 23(1.5%), and suprarenal uptake in 11 (0.7%). Of the 40 studies showing supraclavicular uptake, paravertebral uptake was also seen in 27 (68%), mediastinal uptake in 23 (58%), and suprarenal uptake in 11 (28%). Alternatively, of the 29 studies showing paravertebral uptake, all but 2 studies (93%) also had concomitant supraclavicular uptake. No studies showed isolated mediastinal or suprarenal uptake. All studies with mediastinal uptake also had supraclavicular uptake, and all studies with suprarenal uptake also had paravertebral uptake. Conclusions: Virtually all of mediastinal and suprarenal BAT uptake was associated with supraclavicular and paravertebral uptake, respectively. Nearly all paravertebral uptake coexisted with supraclavicular uptake. Even when CT coregistration is not available, concomitant paravertebral uptake can help differentiate suprarenal uptake and somewhat less typical supraclavicular BAT uptake from malignant uptake, and concomitant supraclavicular uptake can help differentiate mediastinal uptake from malignant uptake.