Pathophysiology
There are three main types of extra-hepatic biliary atresia:
Type I: Atresia is restricted to the common bile duct. Type II: Atresia of the common hepatic duct. Type III: Atresia involves the most proximal part of the bile ducts (>95% of all cases).In approximately 10% of cases, other anomalies may be associated with biliary atresia. The most common of these syndromic forms is BASM and might include heart lesions, polysplenia, situs inversus, absent venae cavae, and a preduodenal portal vein. Progressive cirrhosis is associated with signs and symptoms of portal hypertension, such as esophagogastric varix bleeding, hypersplenism, hepatorenal syndrome, and hepatopulmonary syndrome.In an Egyptian study, abnormally high levels of aflatoxin B1 and to a lesser extent aflatoxin B2 was found in liver tissue and blood of all neonates with biliary atresia. Aflatoxins may cause extensive damage to the hepatocytes leading to hepatitis and damage to bile ducts causing inflammation, adhesions and final obstruction of bile ducts. The affected neonates have a genetic detoxification defect that does not allow them to detoxify these aflatoxins timely or effectively. The babies have homozygous deficiency of glutathione S transferase (GST) M1. The aflatoxin damaged liver cells and bile duct cells are removed by neutrophil elastase and by involvement of immune system mediators such as CCL-2 or MCP-1, tumor necrosis factor (TNF), interleukin-6 (IL-6), TGF-beta,  endothelin (ET), and  nitric oxide (NO). Among these, TGF-beta is the most important pro-fibrogenic cytokine that can be seen in progressive cirrhosis.The cascade of immune involvement to remove damaged hepatocytes and cholangiocytes ushers regeneration.
Published series from Japan, North America, and the UK show that bilirubin levels will fall to normal values in about 50-55% of infants, allowing 40-50% to retain their own liver to reach the age of 5 and 10 years (and beyond). Liver transplantation is an option for those children whose liver function and symptoms fail to respond to a Kasai operation.Recent large-scale studies by Davenport et al. (Annals of Surgery, 2008) show that the age of the patient is not an absolute clinical factor affecting prognosis. The influence of age differs according to the disease etiology—i.e., whether biliary atresia is isolated, cystic (CBA), or accompanied by splenic malformation (BASM).It is widely accepted that corticosteroid treatment after a Kasai operation, with or without choleretics and antibiotics, has a beneficial effect on postoperative bile flow and can clear jaundice, but the dosing and duration of the ideal steroid protocol are controversial. Furthermore, it has been observed in many retrospective longitudinal studies that corticosteroid treatment does not seem to prolong survival of the native liver or transplant-free survival. Epidemiology
Biliary atresia seems to affect females slightly more often than males, and Asians and African Americans more often than Caucasians. It is common for only one child in a pair of twins or within the same family to have the condition. There seems to be no link to medications or immunizations given immediately before or during pregnancy.