Analysis of the Pathomorphology of the Intra- and Extrahepatic Biliary System in Biliary Atresia

OBJECTIVE: Aim of the study was to investigate the pathomorphological changes in the liver and triangular cord of the porta hepatis in biliary atresia and assess the relationship between the degree of differentiation of fibroblasts in the triangular cord of the porta hepatis and the liver fibrosis scores. METHODS: From September 2005 to May 2006, 21 patients with biliary atresia (66+/-20 days old) underwent a Kasai procedure. The liver biopsy and the remnant of the porta hepatis were conserved. Five cases with cholestasis syndrome and 10 cases with choledochal cyst were used as a control group. Liver biopsies were performed in the control group. The micro- and ultrastructure of the liver and the remnant of the porta hepatis were assessed in the biliary atresia and the control group. Ultrastructural features were examined by transmission electron microscopy. The semiquantitative differences in liver fibrosis grading between the biliary atresia and the control group was evaluated with a 3-grade staging system. The degree of differentiation of fibroblasts (FB) in the triangular cord of the porta hepatis was assessed as follows: 1) juvenile type: above 50 % FBs were juvenile, 2) senior type: above 50% FBs were senior, 3) median type: between the former 2 types. The differentiation scores of FB in the porta hepatis were assessed in relation to the liver fibrosis score. RESULTS: 1) The pathological changes with BA are characterized by inflammation and fibrosis in the hepatic portal area. The fibrosis scores in the biliary atresia group (I: 2 cases, II: 12 cases, III: 7 cases) were significantly higher than in the control group (I: 8 cases, II: 5 cases, III: 2 cases; p=0.01. 2) In the biliary atresia group, the extrahepatic biliary system of all cases showed a triangular cord in the porta hepatis. The triangular cord of porta hepatis was characterized by hyperplasia of canaliculi, atresia or stenosis of the bile ducts, inflammation infiltration, cholestasis, and interstitial fibrosis. 3) The ultrastructural features of BA showed active fibroblasts, a loss of microvilli, dense deposits in the hepatocytes and liver sinusoid, and dilatation of canaliculi. 4) The differentiation scores of FB in the porta hepatis were positively related to the liver fibrosis score (p=0.04). CONCLUSION: The main pathological changes of biliary atresia are inflammation and fibrosis in the hepatic portal area. The ultrastructural features of biliary atresia suggested that the differentiation scores of FB in the triangular cord of the porta hepatis were positively related to the liver fibrosis score.