MRI in identifying hepatic steatosis in obese children and relation to ultrasonography and metabolic findings

Objectives: The aim of this study was to identify nonalcoholic fatty liver in obese children by magnetic resonance imaging (MRI) and to compare the findings with the data from ultrasonography and from clinical and laboratory testing. Patients and Methods: Sixty obese children, 6 to 14 years old, underwent hepatic MRI and abdominal ultrasonography. Biochemistry determinations included serum aminotransferases, lipid profile, glucose, and insulin. Anthropometry included body mass index, total and trunk fat, and fat-free mass obtained by dual-energy radiographic absorptiometry. Hepatic steatosis, judged as hepatic fat fraction by MRI, was ≥9%. Results: By MRI, 14 (23%) children had hepatic steatosis; of those, 5 had a fat fraction of 9% to 18%, and 9 had a fat fraction >18%. At univariate analysis, fat fraction was positively associated with being male, serum alanine aminotransferase, aspartate aminotransferase, and γ-glutamyltransferase, body mass index z score, insulin, systolic pressure, and total and trunk fat mass. Hepatic steatosis was independently associated with alanine aminotransferase (P<0.01). Overall, liver echogenicity on ultrasonography correlated well with fat fraction by MRI (correlation coefficient 0.527, P<0.0001). Among the 27 children with increased liver echogenicity, 13 (48%) had hepatic fat fraction ≥9%, and 89% of children with echogenicity graded 2 or 3 had fat fraction >18%. All of the children (n=9) with fat fraction ≥18% had increased liver echogenicity, and in 8 of them it was graded 2 or 3, but the MRI fat fraction ranged greatly (28%-45%). Conclusions: In obese children, nonalcoholic hepatic steatosis may be associated with the metabolic syndrome. Ultrasonography may be valuable in identifying high hepatic fat accumulation, but its ability to identify lower fat accumulation in the liver is scanty compared with MRI. JPGN 47:493-499, 2008.