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Magnetic resonance elastography assessment of fibrosis in children with NAFLD: Promising but not perfect

In the United States, nonalcoholic fatty liver disease (NAFLD)-related cirrhosis is now second among indications for adult liver transplantation. Until recently, detecting histological progression before overt liver dysfunction relied largely on liver biopsy assessment. Over the past decade, however, promising new imaging technologies have emerged for noninvasively detecting advanced fibrosis. The most validated techniques involve measuring liver stiffness through ultrasound (US)-based modalities, vibrationcontrolled transient elastography and shear wave elastography, or through magnetic resonance elastography (MRE). Whereas US elastography is less costly and available at point-of-care (transient elastography), MRE may more accurately detect advanced fibrosis, particularly in adults with NAFLD. MRE is less influenced by abdominal adiposity, assesses a much larger liver volume, and is highly reproducible across readers, field strengths, and imaging platforms. Though highly sensitive and specific for detection of advanced fibrosis in adults with NAFLD, very little is known about the accuracy of MRE in children with NAFLD. To address this gap, Schwimmer et al. conducted a prospective, multicenter, cross-sectional analysis of the performance of MRE in children with NAFLD. They recruited 114 children, ages 8-17 years, at two sites in the nonalcoholic steatohepatitis (NASH) Clinical Research Network. All had undergone clinically indicated liver biopsies with robust phenotyping of histological liver disease. The analysis cohort comprised 90 children (mean age, 13 6 2 years), with 60% having no fibrosis, 27% having stage 1 fibrosis, 7% having stage 2 fibrosis, 6% having stage 3 fibrosis, and 1% having stage 4 fibrosis. Two-dimensional MRE was performed and manually analyzed at two independent reading centers as well as using a novel automated analysis technique. Interreader agreement and correlation between analysis methods were assessed. Twentyfour of the 114 participants (21%) were excluded from analysis, either due to unavailable software at the time of the scan (n 5 7), problems completing the scan (n 5 5), or breathing artifact (n 5 12). The 16% failure rate in attempted MRE is unusually high compared with a <5% MRE failure rate in other published adult and pediatric cohorts. In the present study, the 17 children with excluded MRE had more NASH and stage 3 fibrosis versus the analysis cohort, but no other significant differences. In a consecutive series of liver MRE in 468 children (mean age, 13 6 4 years), age or body mass index did not differ between patients with successful (n 5 450) or unsuccessful MRE (n 5 18), but histological data were not provided. There are several salient findings. First, MRE had comparable sensitivity and specificity for detecting any fibrosis (stage 1) versus no fibrosis compared with adult cohorts. At preset specificity of 90%, the optimal threshold for detecting any versus no fibrosis was 2.69Abbreviations: CI, confidence interval; MRE, magnetic resonance elastography; NAFLD, nonalcoholic fatty liver disease; NASH, nonalcoholic steatohepatitis.