Metabolic Activity in the Visceral and Subcutaneous Adipose Tissues by FDG-PET/CT in Obese Patients

Introduction: The emerging role of the 18F-fluorodeoxyglucose-positron emission tomography/computed tomography in the study of the metabolic activity and inflammation in adipose tissue indicates that it might be a reliable tool to complement the risk stratification in obesity. The aims of this study were the evaluation of 18F-fluorodeoxyglucose uptake by visceral adipose tissues and subcutaneous adipose tissues and to determine eventual differences in patients with and without obesity.
Material and Methods: Retrospective study of adult patients who underwent whole body 18F-fluorodeoxyglucose-positron emission tomography/ computed tomography scanning between July and August of 2016. Statistical analysis: SPSS™ software v.20. Statistical
significance: p < 0.05.
Results: We assessed fluorodeoxyglucose-positron emission tomography/computed tomography scans from 156 patients (58.3% of males) with a mean age of 61.0 ± 14.1 years. Half of the patients had a body mass index ≥ 25.0 kg/m2 and 15.4% (n = 24) were obese. In both groups, the mean 18F-fluorodeoxyglucose uptake was higher in visceral adipose tissues. There were no differences in 18F-fluorodeoxyglucose uptake in visceral adipose tissues between the groups. Obese patients had lower density of adipose tissue,
both in subcutaneous adipose tissues and in visceral adipose tissues. Abdominal circumference and density of visceral adipose tissues
had a positive predictive value in the mean 18F-fluorodeoxyglucose uptake in visceral adipose tissues. 
Discussion: Through a non-invasive test, this study demonstrated a significant higher metabolic activity in visceral adipose tissues in both obese and non-obese patients. According to our results, abdominal circumference was an important determinant in 18F-fluorodeoxyglucose uptake in visceral adipose tissues. We also demonstrated that obese patients had differences in adipose tissue quality.
Conclusion: Our findings reinforce the importance of the adipose tissue quality and distribution for metabolic risk stratification.

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