Nonalcoholic fatty liver disease (NAFLD) is a clinicohistopathologic entity that includes a spectrum of conditions characterized histologically by macrovesicular hepatic steatosis in those who do not consume alcohol in amounts generally considered harmful to the liver. 
Steatohepatitis (nonalcoholic steatohepatitis or NASH)
Macrovesicular or mixed predominantly macro/microvesicular steatosis with evidence of hepatocyte ballooning degeneration, mild diffuse lobular mixed acute and chronic inflammation, and perivenular perisinusoidal collagen deposition.Image 2
Wound healing response in which damaged regions of chronic inflammatory disease are encapsulated by extracellular matrix or scar tissue. In its initial stages, fibrosis is thought to be reversible to some degree, but in the late stages it is felt to be irreversible. In NASH, fibrosis is staged 0 through 4.
Histologic definition connoting the last stage of progressive hepatic fibrosis. Characterized by the distortion of hepatic architecture and the formation of regenerative nodules. It is traditionally believed to be an irreversible condition.Image 3
NASH-associated end-stage liver disease
Term used to describe the stage at which patients with cirrhosis develop clinical complications. A majority of the complications are sequelae and manifestations of advanced fibrosis with portal hypertension and decreased synthetic function of the liver. They include ascites, portosystemic encephalopathy, variceal bleeding, hepatocellular carcinoma, and the hepatorenal and hepatopulmonary syndromes.
Simple steatosis (felt to be nonprogressive).
Steatosis plus lobular inflammation (probably benign, not considered to be NASH).
Steatosis, lobular inflammation, and ballooning degeneration. This is NASH without fibrosis (may progress to cirrhosis and liver failure).
Steatosis, ballooning degeneration, and fibrosis or Mallory bodies. This is NASH with fibrosis (may progress to cirrhosis and liver failure).