Background/Purpose: The aim of this paper was to investigate the mechanism of long-term biliary drainage after Kasai portoenterostomy by clinicopathologic study of hepatic morphology in explanted livers.Methods: Explanted livers from 13 consecutive children undergoing transplantation for biliary atresia were examined in detail using a standardized protocol.Group 1 (n = 6) had no Kasai procedure before transplantation at a median age of 8 m.Group 2 (n = 4) were transplanted at a median age of 10 m after a failed Kasai portoenterostomy.Group 3 (n = 3) had a successful Kasai but required transplantation for complications of chronic liver disease at 12-14 years.Pathology findings were correlated with hepatic morphology determined by pretransplant magnetic resonance imaging.Results: Large perihilar regenerative nodules (8-14 cm diameter) were observed in 2 patients after successful Kasai portoenterostomy, less well-de-fined perihilar nodules in group 2 patients, and no regenerative nodules in group 1.Microscopically, group 1 had diffuse biliary cirrhosis with evidence of progressive ductopenia during infancy.In group 2, perihilar regenerative nodules showed variable portal fibrosis but no cirrhosis and bile ducts were present with 68%-100%of hepatic arteries; in peripheral cirrhotic areas, bile ducts were absent in patients older than 9 m.The perihilar regenerative nodules in group 3 patients had a noncirrhotic architecture with preserved bile ducts, but the peripheral parenchyma was cirrhotic; one patient had diffuse macronodular cirrhosis.These morphologic findings correlated well with magnetic resonance images, highlighting the preservation of relatively normal perihilar liver architecture after successful Kasai portoenterostomy.Conclusions: Unoperated biliary atresia is associated with progressive intrahepatic ductopenia leading to diffuse biliary cirrhosis.Kasai portoenterostomy can result in the growth of large perihilar regenerative nodules, probably as a consequence of surviving intrahepatic ducts in this region.In some patients, long-term success after Kasai portoenterostomy may depend on hyperplasia of the perihilar liver. Background / Purpose: The aim of this paper was to investigate the mechanism of long-term biliary drainage after Kasai portoenterostomy by clinicopathologic study of hepatic morphology in explanted livers. Methods: Explanted livers from 13 consecutive children undergoing transplantation for biliary atresia were examined in detail using a standardized protocol. Group 1 (n = 6) had no Kasai procedure before transplantation at a median age of 8 m. Group 2 (n = 4) were transplanted at a median age of 10 m after a failed Kasai portoenterostomy. Group 3 (n = 3) had a successful Kasai but required transplantation for complications of chronic liver disease at 12-14 years. Pathology findings were correlated with hepatic morphology determined by pretransplant magnetic resonance imaging. Results: Large perihilar regenerative nodules (8-14 cm diameter ) were observed in 2 patients after successful Kasai portoenterostomy, less well-de-fined perihilan nodules in group 2 patients, and no regenerative nodules in group 1. Microscopically, group 1 had diffuse biliary cirrhosis with evidence of progressive ductopenia during infancy.In group 2, perihilar regenerative nodules showed variable portal fibrosis but no cirrhosis and bile ducts were presented with 68% -100% of hepatic arteries; in peripheral cirrhotic areas, bile ducts were absent in patients older than 9 m. The perihilar regenerative nodules in group 3 patients had a noncirrhotic architecture with preserved bile ducts, but the peripheral parenchyma was cirrhotic; one patient had diffuse macronodular cirrhosis.These morphologic findings correlated well with magnetic resonance images, highlighting the preservation of relatively perihilar liver architecture after successful Kasai portoenterostomy. Conclusions: Unoperated biliary atresia is associated with progressive intrahepatic ductopenia leading to diffuse biliary cirrhosis. Kasai portoenterostomy can result in the growth of large perihilar regenerative nodules, probably as a consequence of surviving intrahepatic ducts in this region. Some patients, long-term success after Kasai portoenterostomy may depend on hyperplasia of the perihilar liver.