Diagnosis and Assessment of NAFLD: Definitions and Histopathological Classification

Nonalcoholic fatty liver disease (NAFLD) comprises a spectrum of clinical and histopathological changes including "simple" steatosis, steatosis with inflammation, steatohepatitis, cirrhosis, and hepatocellular carcinoma. It was initially described in the context of drug-induced liver injury and acute liver disease following jejunoileal bypass surgery, but since the early 1980s it has been widely acknowledged as the hepatic manifestation of metabolic syndrome. It now represents a burgeoning public health crisis and is fast becoming the main indication for liver transplantation in some parts of the world. Its true incidence and prevalence are unknown, although estimates have been made from large imaging studies. Liver biopsy interpretation is still regarded as the gold standard for making accurate diagnoses in NAFLD, but sampling limitations are recognized. Furthermore, clear definitions for key histopathological components have been lacking, resulting in significant interobserver variations in making a diagnosis of steatohepatitis. In this review the authors consider some aspects of classification and variant forms of NAFLD such as that occurring in children. They provide an update on grading and staging systems and histopathological prognostic factors, and address the role of liver biopsy in contemporary clinical care of patients with NAFLD.