Histopathology of cholestasis
Cholestasis may be extrahepatic or intrahepatic in origin. The block in bile secretion may be complete or incomplete to variable extent. Complete cholestasis occurs in case of primary parenchymal disease (intrahepatic cholestasis) or total obstruction of extrahepatic bile ducts (extrahepatic cholestasis). Incomplete block in bile secretion is due to incomplete obstruction of intra- or extrahepatic bile ducts (intra- or extrahepatic cholestasis or both). Histologically, it is useful to distinguish between bilirubionstasis and cholate-stasis. Complete secretory block causes as early changers: bilirubinostasis (in hepatocytes, canaliculi and Kupffer cells) in acinar zone 3, and "ductular reaction" in acinar zone 1. The latter refers to an increase in periportal ductular profiles, associated with neutrophil infiltration. With longer duration of cholestasis, further lesions ensue: feathery degeneration of hepatocytes due to retention of detergent bile acids, cholestatic liver cell rosettes representing a shift from hepatocellular to biliary differentiation, xanthomatous cells reflecting hyperlipidemia, cholate stasis in acinar zone 1 due to overload of membrane-damaging bile acids, eventually paraportal bile infarcts, and progressive ductular reaction. The latter may be due to multiplication of pre-existing ductules, to metaplasia of periportal hepatocytes, or to activation of progenitor cells. It is invariably associated with periductular fibrosis: the pacemaker for increasing matrix deposition, resulting in biliary fibrosis and eventually in true biliary cirrhosis. Incomplete cholestasis (e.g. PBC, PSC) is characterized by absence of bilirubinostasis during long periods of time, whereas the afore mentioned features of chronic cholestasis do appear. Hence follows that the most reliable markers of chronic incomplete cholestasis are cholate stasis, cholestatic rosettes and ductular reaction. Bilirubinostasis is only a late and often ominous sign.
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