Brown fat on PET/CT

Case contributed by Dr Katia Kaplan-List

Presentation

50 year-old female referred for initial staging of a known rectosigmoid carcinoma.

Patient Data

Age: 50
Gender: Female
Nuclear medicine

There is diffuse symmetric bilateral FDG uptake within the mediastinum, neck and upper chest, paraspinal muscles and retroperitoneum corresponding to brown fat activity. The soft tissue uptake is clearly localized within the fatty tissue as demonstrated by PET/CT co-registration.

Case Discussion

Nonpathologic supraclavicular uptake of 18F-FDG seen with PET was initially believed to be predominantly muscular uptake because it could be suppressed with muscle relaxants and sedatives. However, with the introduction of FDG PET integrated with CT (PET/CT), Cohade et al. in 2003 used CT to correlate focal FDG supraclavicular uptake to tissue fat density rather than solely muscle and termed the finding as uptake in supraclavicular area fat or “USA fat.”

Several studies suggested this tissue to be brown fat versus white fat because the tracer uptake could be well correlated with the physiology of brown fat, exemplified by the increased uptake in response to cold exposure.

FDG uptake in fatty tissue was observed in well-defined patterns consistent with the typical locations of brown fat.

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Case information

rID: 42971
Case created: 16th Feb 2016
Last edited: 18th Feb 2016
Inclusion in quiz mode: Included

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