Biliary atresia is a severe cholestatic disease characterized by progressive obliteration and fibrosis of extrahepatic bile ducts in the neonatal period. If untreated, it leads to biliary cirrhosis and death — it is the most common indication for pediatric liver transplantation. Incidence is 1:8,000-18,000 live births, more common in Asian populations. Kasai portoenterostomy (hepatoportoenterostomy) must be performed within the first 60 days — success rate markedly decreases with delayed surgery. Cardinal imaging findings include triangular cord sign (triangular-shaped fibrotic tissue anterior to portal vein bifurcation), absent or anomalous gallbladder, and absence of intrahepatic bile duct dilatation.
Age Range
0-1
Peak Age
-
Gender
Equal
Prevalence
Rare
Although the pathogenesis of biliary atresia is not fully elucidated, viral infection-triggered (reovirus, CMV, rotavirus) autoimmune mechanism is the most accepted hypothesis. In the perinatal period, viral damage to bile duct epithelium → immune-mediated progressive inflammation → periductal fibrosis → obliteration of duct lumen. Extrahepatic bile ducts (choledochus, hepatic duct, cystic duct) become fibrotic cords — bile flow completely stops. Bile accumulation (cholestasis) leads to hepatocyte damage and rapidly developing periportal fibrosis. In imaging, the triangular cord sign is the US appearance of this fibrotic remnant — seen as a triangular echogenic structure anterior to portal vein bifurcation at porta hepatis (>4 mm thickness). Gallbladder is usually absent or very small and non-contractile because the cystic duct is also atretic. Intrahepatic bile ducts are NOT dilated because progressive fibrotic obliteration of ducts does not allow luminal expansion — this feature distinguishes biliary atresia from other neonatal obstructive causes.
Triangular echogenic structure >4 mm thickness anterior to portal vein bifurcation at porta hepatis — represents fibrotic tissue of atretic extrahepatic bile duct remnant. Most specific US finding for biliary atresia (98% specificity). Should be evaluated in both sagittal and transverse planes.
Triangular echogenic structure anterior to portal vein bifurcation at porta hepatis — triangular cord sign. Thickness >4 mm on sagittal and transverse sections is considered diagnostic. This structure represents the fibrotic tissue of atretic extrahepatic bile duct remnant. Sensitivity 73-100%, specificity 98% — most reliable US sign for biliary atresia. Visualization of the irregular echogenic structure immediately anterior to the portal vein branching point is critical.
Report Sentence
Triangular cord sign with >4 mm thickness anterior to portal vein bifurcation at porta hepatis is noted, consistent with biliary atresia.
Gallbladder is not visualized despite fasting or abnormally small (<15 mm, microgallbladder), irregularly shaped, and non-contractile. In normal neonates, gallbladder is >15 mm while fasting and contracts after feeding. In biliary atresia, the cystic duct is also atretic so gallbladder cannot develop a lumen. The term 'ghost gallbladder' is used — only echogenic tissue is seen in the gallbladder fossa, no anechoic lumen.
Report Sentence
Gallbladder is not visualized despite fasting / microgallbladder is identified; may be consistent with biliary atresia.
Hepatobiliary scintigraphy (HIDA — Tc-99m IDA derivatives) shows normal liver uptake but no bowel excretion on delayed images up to 24 hours. Phenobarbital premedication (5 mg/kg/day for 5 days) is given — reduces false positives by increasing bile flow. In biliary atresia, bile ducts are obliterated so radiopharmaceutical cannot pass from hepatocytes to biliary tract — renal excretion to kidneys is seen. In neonatal hepatitis syndrome, bowel passage is seen on delayed images — this is the most important differential criterion.
Report Sentence
Normal liver uptake on hepatobiliary scintigraphy but no bowel excretion on 24-hour delayed images; consistent with biliary atresia.
Extrahepatic bile duct system (choledochus, hepatic ducts, cystic duct) is not visualized on MRCP — in normal neonates these structures are visible even if thin. Gallbladder is not visualized if there is no fluid in its lumen. Intrahepatic bile ducts may also not be visualized because neonatal ducts are very thin. However, MRCP is considered less reliable than US and scintigraphy for biliary atresia diagnosis — not a primary diagnostic method but useful for preoperative anatomic mapping.
Report Sentence
Extrahepatic bile duct system is not visualized on MRCP; may be consistent with biliary atresia.
Increased hepatic artery diameter and elevated hepatic artery/portal vein diameter ratio (>0.45) on Doppler US. Periportal fibrosis and inflammatory hyperemia in biliary atresia increase hepatic arterial flow — as compensatory mechanism to balance decreased portal flow. Hepatic artery appears enlarged with increased arterial flow detected in periportal areas. This finding is not diagnostic but has value as an additional supportive sign.
Report Sentence
Increased hepatic artery diameter and elevated hepatic artery/portal vein ratio are noted, which may be associated with periportal fibrosis in the context of biliary atresia.
Criteria
Distal choledochal atresia; proximal ducts patent (5%)
Distinct Features
Most favorable type for Kasai surgery; gallbladder may be normal
Criteria
Atresia at hepatic duct level; may be associated with cystic dilatation (3%)
Distinct Features
If cystic structure is seen at porta hepatis, must be distinguished from choledochal cyst
Criteria
Complete obliteration of entire extrahepatic bile duct system (90%+)
Distinct Features
Triangular cord sign most prominent; gallbladder micro or absent; worst prognosis after Kasai
Distinguishing Feature
Choledochal cyst shows cystic dilatation of extrahepatic bile duct + normal gallbladder; biliary atresia shows non-visualized duct + absent/micro gallbladder
Distinguishing Feature
Acute cholangitis shows bile duct dilatation + wall thickening; biliary atresia has no duct dilatation
Distinguishing Feature
Cholelithiasis shows echogenic stone + acoustic shadow in gallbladder and is very rare in neonates; biliary atresia shows absent gallbladder
Distinguishing Feature
Caroli disease shows segmental saccular dilatation of intrahepatic ducts ('central dot sign'); biliary atresia has no duct dilatation
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralBiliary atresia is a pediatric surgical emergency — Kasai portoenterostomy must be performed within the first 60 days. Success rate is 80%+ when surgery is done within 30 days, drops below 20% after 60 days. 70-80% of Kasai-failed cases need liver transplantation within the first 2 years. Delay in diagnosis directly affects prognosis — if neonatal jaundice persists beyond 2 weeks with elevated conjugated bilirubin, urgent US and scintigraphy should be performed.
Biliary atresia is the most critical surgical cause of neonatal cholestasis. Kasai portoenterostomy must be performed within 60 days — success rates decline rapidly with delayed surgery. If surgery fails, liver transplantation is the only option. Early US evaluation with triangular cord sign detection is life-saving.