Ultrasound Findings in Biliary Atresia
The most important ultrasound findings for diagnosing biliary atresia are abnormal gallbladder morphology (present in nearly all cases), the triangular cord sign (85% sensitive, 97% specific), and nonvisualization of the common bile duct.
Key Diagnostic Features
Gallbladder Abnormalities
- Abnormal gallbladder morphology is the most consistent finding, present in 100% of biliary atresia cases 1
- Gallbladder may be absent, small (<1.5 cm length), irregular in shape, or have abnormal contractility 2
- Sonographic absence of the gallbladder has 53% sensitivity but 94% specificity for biliary atresia, with a 96% positive predictive value 3
- A normal-appearing gallbladder does NOT exclude biliary atresia, as morphologic abnormalities can be subtle 2
Triangular Cord Sign
- The triangular cord sign demonstrates 85% sensitivity and 97% specificity for biliary atresia 2
- This represents periportal fibrosis appearing as an echogenic triangular or tubular structure anterior to the portal vein bifurcation 4
- Cutoff thickness of >3-4 mm is diagnostic 2
- The sign may show hypoechoic or cystic portions within the triangular cord in 11% of cases 1
Bile Duct Visualization
- Absence of the extrahepatic bile duct at the liver hilum ("duct at the hilum") has 100% sensitivity and 94% specificity 5
- Nonvisualization of the common bile duct is a highly specific finding 2
- A systematic four-step approach focusing on location, position, length, and absence of blood flow can identify this finding efficiently, often in <5 minutes 5
Vascular Findings
- Hepatic artery enlargement occurs in 73% of biliary atresia cases 1
- Hepatic subcapsular arterial flow is present in 23% of patients and shows high diagnostic performance 1, 2
- Increased hepatic arterial flow reflects compensatory changes from biliary obstruction 4
Additional Findings
- Cysts in the porta hepatis are present in 15% of cases 1
- Polysplenia syndrome accompanies biliary atresia in 11% of patients 1
- Look for associated anomalies including situs abnormalities and vascular malformations 4
Clinical Pitfalls
Ultrasound findings may be inconclusive in early neonatal period, requiring repeat imaging or more invasive testing 5. The triangular cord sign's diagnostic accuracy varies with cutoff thickness used (3 mm vs 4 mm), which significantly affects study heterogeneity 2. Nonidentification of the gallbladder ranges from 0-53% across studies, reflecting operator dependence 2.
Ultrasound remains the first-line imaging modality for investigating neonatal cholestasis and establishing suspicion for biliary atresia, which then indicates laparotomy with intraoperative cholangiography 1. The examination is non-invasive, portable, relatively inexpensive, and can often be performed in feeding infants without requiring fasting 5.