Pathology of septum formation in primary biliary cirrhosis: a histological study in the non-cirrhotic stage.

Bridging or incomplete septum formation, an important step leading to cirrhosis in various chronic progressive liver diseases, was examined in 231 liver biopsy specimens of primary biliary cirrhosis (non-cirrhotic stage. Incomplete septa from the enlarged portal tracts and portal to portal bridges were frequent and appeared first, while portal to central ones appeared subsequently and became frequent in the liver specimens with changes resembling cirrhosis. These septa were divided into four types histologically: ductular, lymphocytic, loose connective tissue and fibrous type. More than one type was usually found in the same specimen. The pathology of the first three types was similar to and frequently continuous with that of neighbouring periportal regions, suggesting that most of these septa were formed by the extension of periportal destructive processes. The fibrous type might be an advanced form of the other three types. Incomplete septa seemed to pinch off part of the hepatic parenchyma in a hepatic lobule; this was followed by an unusual enlargement of the portal tracts and an approximation of portal tracts and central veins. There were perivenular hepatocellular necroses on occasion. Progression of periportal hepatocellular damage may lead to septum formation and finally progress to cirrhosis, in primary biliary cirrhosis. The significance of perivenular necroses remains speculative.