Background: The function of adipose tissue is determined by its location and type (white vs. brown fat). In adults, periaortic fat and white fat promote metabolic disease. However, little is known about periaortic fat in children. 

Objectives: Using a novel research tool, free-­breathing magnetic resonance imaging (MRI), this study aimed to: 1. measure periaortic fat volume and content and 2. investigate correlations between periaortic fat and clinical characteristics in children.

Methods: Healthy and overweight (body mass index ≥85th percentile) children were eligible. Periaortic adipose tissue volume and proton ­density fat fraction (PDFF), a biomarker for adiposity content, were measured along the abdominal aorta using free­-breathing MRI.

Results: Healthy children (n=21, median age 11.4 [IQR 9.9­-14.1]) and overweight children (n=26, age 14.9 [11.9-­16.2]) completed the study (p<0.01). In the overweight group, 62% had NAFLD and their median [IQR] body mass index z-score was greater than the healthy group (3.0 [0.8-4.0] vs. -0.3 [0.8-4.0], p<0.001). In comparison to healthy children, periaortic adipose tissue volume was greater in overweight children (5.2 cm3 [3.6-7.4] vs. 3.3 cm3 [2.9-­4.2], p=0.0005). Likewise, periaortic adipose tissue PDFF (54% [44-63] vs. 33% [29­-38], p<0.0001) and hepatic PDFF (16.9% [2.9-22.8] vs 2.6% [2.2-3.3], p<0.001) were significantly greater in overweight vs. healthy children. Adipose tissue volume and PDFF correlated with body mass index z-­score (r=0.65 and r=0.79, p<0.001 each) and hepatic PDFF (r=0.54 and r=0.67, p<0.001 each). In contrast, periaortic adipose tissue volume and PDFF were negatively correlated with serum high density lipoprotein (r=-0.66 and r =-0.56, p<0.05 each).

Conclusions: In this study, overweight children with NAFLD had increased periaortic fat volume and PDFF and hepatic PDFF compared to their healthy counterparts. A higher fat content in the periaortic region (i.e., PDFF) may indicate increased susceptibility to metabolic diseases.