Pathology of nonalcoholic steatohepatitis

Current discussions in pathology include identification of lesions of concern for progression, reproducible methods of diagnosis and semiquantification of lesions, and appropriate nomenclature. Matteoni et al. proposed NAFLD types 1-4 based on long-term outcome studies; Brunt et al. proposed a system of grading and staging for NASH that follows methods of separate assessment for necroinflammatory lesions (grade) and fibrosis (stage) accepted in other forms of non-biliary chronic liver disease. Recently, the Pathology Committee of the NIDDK NASH Clinical Research Network has proposed a system of evaluation that encompasses the entire spectrum of NAFLD from steatosis to steatohepatitis with fibrosis for use in upcoming treatment trials. And, just as the clinician cannot distinguish steatosis and steatohepatitis, the pathologist cannot discern if alcohol abuse may be an underlying cause of the lesions. Proposed nomenclature to align with either extant terminology in other forms of chronic liver disease, or to align with our knowledge of underlying cause(s) (such as metabolic syndrome) will be discussed.