When interpreting a liver biopsy, it is helpful to first identify a portal triad (bile duct, hepatic artery, portal vein). This is often termed, Zone 1 by the pathologists, and the periportal region is labeled with a ‘1’ in the histologic specimen above.
Zone 2 connotates the hepatic lobule, or the redundant parenchyma of hepatocytes that account for the majority of the specimen. When portal inflammation extends into Zone 2, for example, it is termed ‘interface hepatitis’ and is associated with autoimmune hepatitis and sometimes with hepatitis C. When fibrosis predominates in Zone 2, it is commonly from a toxic-metabolic injury, such as from NASH.
Zone 3 refers to the area near the central vein. It is commonly involved when there is drug injury, since the metabolizing enzymes are concentrated here. This region also has the lowest concentration of pO2 and is particularly susceptable to ischemic injury. Cardiac/hemodynamic disturbances like congestion or outflow obstruction also will manifest here.