Biliary Atresia Definition Biliary atresia (BA) is a progressive, idiopathic, fibro-obliterative disease of the extrahepatic biliary tree that presents with biliary obstruction exclusive in the neonatal period. Although the overall incidence is low (about 1:10,000 to 1:20,000 live births), BA is the most common cause of neonatal jaundice for which surgery is indicated and the most common indication for liver transplantation in children. Infants with BA can be grouped into 3 categories (1): 1. BA without major malformations - sometimes referred to as isolated, non-syndromic or perinatal BA (without major malformations), this pattern occurs in ~80-85% of infants with BA. 2. BA in association with laterality malformations – also known as syndromic biliary atresia, fetal-embryonal biliary atresia, or Biliary Atresia Splenic Malformation (BASM), this pattern occurs in about 10% of infants with BA, and includes the clinical presence of laterality defects. 3. BA in association with at least one major malformation – this pattern occurs in about 5-10% of infants with BA who have associated anomalies most commonly manifested in the cardiovascular (71%), genitourinary (47%) and gastrointestinal (24%) systems and without laterality defects. Etiology and Pathogenesis The underlying cause or trigger of BA remains unknown. A number of mechanisms has been hypothesized and detailed in several recent excellent reviews (2, 3). These include viral, toxin-induced, vascular, genetic predisposition, abnormal morphogenesis/development, and autoimmune/ immune dysregulation. Viral Etiologies: Two animal models of BA which utilize virus (the reovirus mouse model and more recently the rotavirus mouse model) as well as time-space clustering of BA cases in humans support a possible viral etiology. The livers of afflicted children exhibit many of the inflammatory responses characteristic of viral infection including activated macrophages, CD4 and CD8 T cells, interferon gamma, cytokines such as tumor necrosis alpha, and IgM and IgG antibodies (4, 5). To-date, a specific virus has not been implicated, with studies failing to consistently identify associations with specific viral infections. including cytomegalovirus, reovirus, and Group C rotavirus. Toxic etiologies – The clustering of cases of BA is also consistent with the possibility of a toxin-mediated inflammatory response (6). Recently, a toxin, biliatresone, a plant isoflavenoid found in in Australia, has been implicated in the development of BA in sheep, (7) however no human associations have been described. Vascular etiology - while studies have described both hyperplasia and hypertrophy of the hepatic artery supporting a vascular-mediated etiology for BA, these findings could be secondary to the characteristic hepatic fibrosis and cirrhosis (2). Genetic etiologies – Genetic factors may play a causative role in the small subgroup of patients with BASM malformations. A transgenic mouse with a recessive deletion of the inversin (INV) gene provides an animal model for BASM, displaying situs inversus and extrahepatic biliary obstruction. However, genetic factors may not play a direct causative role in the development of most cases of BA – as suggested by the observation that monozygotic twins usually have a discordant phenotype – but rather play a role in disease susceptibility. Association studies have identified a few genomic loci with increased susceptibility to BA. Epigenetic factors have also been postulated as important factors impacting biliary development and the pathogenesis of BA. Both micro RNA and DNA methylation have been studied in animal models and humans with BA. Abnormal morphogenesis - is supported by the observation of ductal plate malformations (persistence of ductal plates postnatally) in the diagnostic liver biopsies from BA infants (8). The presence of extrahepatic anomalies including situs inversus, cardiac abnormalities, splenic malformation (including asplenia, polysplenia or double spleen), preduodenal portal vein and annular pancreas support the concept of defective embryogenesis targeting or causing obstruction of extrahepatic bile ducts. Mutations in the CFC1 gene, which encodes cryptic protein and is involved in determining laterality during fetal development, have been linked to BA patients with laterality defects (9). There is both human and animal data in support of a role of immune dysregulation. These data include increased expression of intercellular adhesion molecules, increased frequency of the HLA-B12 allele, oligoclonal expansion of lymphocytes, and prevention of experimental biliary atresia in mice by loss of a2ß1 integrin, interferon-?, CD8+ cells, and NK cells (10, 11). Recent work has demonstrated a significant upregulation of the Hedgehog pathway in BA causing epithelial to mesenchymal transition, and leading to fibrosis (12). It is entirely possible and perhaps most likely, that BA is of diverse etiology – secondary to dysmorphogenesis in the minority and one or more viral infections in an immunologically and genetically susceptible host in the majority. The preliminary mouse and human data that have been generated based on hypotheses of autoimmune/autoreactive response that results in injury to the bile duct are the basis for the current trial of IVIg in infants with biliary atresia being conducted by the ChiLDReN consortium (13). Clinical Features Most infants with BA are born at full term, have a normal birth weight and initially thrive and seem healthy. Jaundice is almost always the first sign of BA, although initial jaundice is possibly seen only in the sclerae. The onset of jaundice occurs any time from birth up to 8 weeks of age, and it is highly unlikely to appear later. Physiologic jaundice is dominated by indirect/unconjugated bilirubin and generally clears by 2-3 weeks. Most infants with BA develop acholic stools; however, acholic stools often go unrecognized because the stools are pale, but not white and the stool color can vary on a daily basis. To help parents distinguish between normal and acholic stools, printed stool “color cards” and a free smartphone application (PoopMD for iphone or Android) have been developed (14). Most infants have dark urine because of bilirubin excretion into the urine. However, this often is not recognized by parents, who may not realize that infant urine should not stain a diaper yellow. If the jaundice has gone unnoticed, and the child’s disease has progressed, there may be a firm, enlarged liver and splenomegaly. Clues for infants with the fetal-embryonal form of BA include asplenia or polysplenia on ultrasound, and evidence of congenital heart disease. Diagnosis Earliest diagnosis of BA is important because the prognosis is closely related to timing of Kasai portoenterostomy (HPE). The evaluation process involves a series of laboratory and radiographic imaging studies, followed by cholangiogram. The order of diagnostic investigations may be prioritized based on testing for treatable conditions first – these include biliary obstruction, infections, and some metabolic diseases. Some diseases, such as Alagille syndrome or alpha-1-antirypsin deficiency, can mimic many of the findings seen in BA. Laboratory studies - Serum direct/conjugated bilirubin may be elevated from shortly after birth (15). Typically, serum gamma glutamyltranspeptidase is markedly elevated. Infants with mildly elevated conjugated or direct bilirubin levels in the perinatal period should be followed closely and evaluated for the possibility of BA. The presence of hypoalbuminemia, coagulopathy and thrombocytopenia may indicate significant progression of disease. Abdominal ultrasound– Evaluation of biliary anatomy begins with an ultrasound and Doppler study, which can quickly exclude other anatomic causes of cholestasis, such as a choledochal cyst. In infants with BA, the gallbladder is usually hypoplastic, irregular in shape, or absent. When a detailed ultrasonographic protocol is utilized, additional features can be identified to support a diagnosis of biliary atresia, including the “triangular cord” sign, although this can be operator dependent. The ultrasonographic findings of polysplenia/asplenia, intestinal malrotation, interrupted IVC or midline liver should prompt immediate evaluation for BA. Cholangiogram - The gold standard for diagnosing BA remains intra-operative cholangiogram by an experienced pediatric surgeon, with the diagnosis established when contrast injected into the biliary remnant fails to pass into the intestine, when there is no lumen in the biliary tract remnant to inject with contrast, or when the biliary tract is not visible at all. There is significant variability between different centers on the role, use and timing of other diagnostic tests such as hepatic scintigraphy (HIDA scan), magnetic resonance cholangiopancreatography (MRCP) and endoscopic retrograde cholangiopancreatography (ERCP). Such decisions should never delay timely evaluation of infants still jaundiced after 14 days of life for direct/conjugated hyperbilirubinemia and referral to a pediatric liver center if cholestasis is present for earliest decision making on the role and timing of liver biopsy and laparotomy for intraoperative cholangiogram with potential surgical intervention with hepatoportoenterostomy (HPE). Treatment Surgical Therapy - Earliest diagnosis of BA is important because the prognosis is closely related to timing of HPE. After the HPE operation, the bilirubin and other laboratory parameters are monitored over time to determine