Nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) significantly contributes to the morbidity and mortality of large proportions of the population across all age ranges, which will continue for the foreseeable future. Since NAFLD and nonalcoholic steatohepatitis were originally described, understanding of pathogenesis, relationships to insulin resistance and the metabolic syndrome, and histopathologic lesions has progressed. However, no clinical or imaging parameters can yet accurately predict inflammatory activity or fibrosis stage across the spectrum of disease. Liver needle biopsy interpretation remains essential in this role; liver biopsy evaluation is also needed for recognition of concurrent (or alternate) liver disease processes. Thus, an understanding of the histologic spectrum of findings in NAFLD and the methods of semiquantitative evaluations used are required for pathologists who sign out liver biopsies. This article describes histologic findings, and provides insights into the pathologic processes and clinical implications across the spectrum of NAFLD.