Imaging patterns of fatty liver in pediatric patients

Fatty liver can present as focal, diffuse, heterogeneous, and multinodular forms. Being familiar with various patterns of steatosis can enable correct diagnosis. In patients with equivocal findings on ultrasonography, magnetic resonance imaging can be used as a problem solving tool. New techniques are promising for diagnosis and follow-up. We review imaging patterns of steatosis and new quantitative methods such as proton density fat fraction and magnetic resonance elastography for diagnosis of nonalcoholic fatty liver disease in children.Nonalcoholic fatty liver disease (NAFLD) is as widely encountered in children as in adults, with an estimated prevalence of 9.6% (1). It occurs due to accumulation of triglyceride in hepatocytes without alcohol ingestion. Nonalcoholic steatohepatitis (NASH) was first defined in children in 1983 (2). NAFLD includes a broad range of clinicopathologic features ranging from simple steatosis (fat with inflammation and/or fibrosis), steatohepatitis/NASH to cirrhosis. Some other diseases of liver can also cause hepatic steatosis including hepatitis B and C, Wilson’s disease, α-1-antitrypsin deficiency, autoimmune hepatitis, drug-induced liver injury (valproate, methotrexate, tetracycline, amiodarone, and prednisone), and total parenteral nutrition (3). Furthermore, fatty liver is a risk factor for cirrhosis, diabetes, and cardiovascular disease.In clinical practice, the diagnosis of NAFLD is made by increased serum ALT and/or presence of enlarged echogenic liver in ultrasonography. Being overweight or obese, and/or insulin resistance are highly indicative but not absolutely necessary for diagnosing NAFLD (4). The gold standard for diagnosis is liver biopsy, which additionally provides semi-quantitative analysis of NASH damage in children (5). It is an expensive, invasive procedure with a risk of morbidity (0.06%–0.35%) and mortality (0.01%–0.1%) (6).The evaluation of liver fat in children via noninvasive imaging modalities is needed to avoid complications of biopsy and for follow-up. Main imaging modalities for the assessment of pediatric NAFLD are ultrasonography (US) and magnetic resonance imaging (MRI). Computed tomography is the other imaging method for liver fat assessment, but ionizing radiation is a major drawback in children (7). Assessment of fat accumulation may cause diagnostic dilemmas and confusion due to manifestations with unusual structural patterns and imaging appearance of the liver. This article reviews the histopathology of pediatric NAFLD, radiologic evaluation and different structural patterns of childhood NAFLD/NASH on US and MRI. We also discuss diagnostic pitfalls and briefly review new imaging techniques.