Triangular Cord Sign in Biliary Atresia
The triangular cord (TC) sign is a triangular or tubular-shaped echogenic density visualized on ultrasound at the porta hepatis, immediately cranial to the portal vein bifurcation, representing the fibrous obliterated ductal remnant characteristic of biliary atresia. 1, 2
Anatomic Basis
The TC sign corresponds to the cone-shaped fibrous tissue consistently found at the porta hepatis during Kasai hepatoportoenterostomy procedures in biliary atresia patients—this fibrous remnant represents the obliterated extrahepatic bile ducts and is never seen in other cholestatic conditions like neonatal hepatitis. 2
Objective Diagnostic Criteria
The TC sign is objectively defined as an echogenic anterior wall of the right portal vein (EARPV) measuring greater than 4 mm thickness on longitudinal ultrasound scan. 3
- Mean EARPV thickness in biliary atresia is 5.39 mm compared to 2.17 mm in neonatal hepatitis (P <0.05). 3
- This 4-mm cutoff provides 80% sensitivity, 98% specificity, and 94% positive predictive value for diagnosing biliary atresia. 3
Diagnostic Performance
The TC sign demonstrates superior diagnostic accuracy compared to other ultrasound findings:
- Overall diagnostic accuracy of 95% with 93% sensitivity and 96% specificity when comparing biliary atresia to neonatal hepatitis and other causes of infantile cholestasis. 4
- The TC sign was present in 27 of 29 infants (93%) with confirmed biliary atresia and only 1 of 26 infants (4%) with neonatal hepatitis or other cholestatic causes. 4
- This significantly outperforms gallbladder length assessment (71% accuracy) and gallbladder contraction evaluation (77% accuracy). 4
Clinical Application Algorithm
When TC sign is visualized: No further diagnostic studies are necessary—proceed directly to exploratory laparotomy for Kasai procedure. 2
When TC sign is not visualized:
- Perform hepatobiliary scintigraphy to assess bile duct patency and intestinal excretion of isotope. 2
- If scintigraphy shows no intestinal excretion, proceed to percutaneous liver biopsy. 2
- Critical caveat: Even with negative TC sign and liver biopsy confirming neonatal hepatitis, maintain close ultrasound follow-up or consider early exploration if clinical suspicion for biliary atresia remains high, as TC sign can appear on serial imaging in evolving cases. 2
Important Clinical Pitfalls
One documented case initially showed absent TC sign with liver biopsy suggesting neonatal hepatitis, but repeat ultrasound 40 days later revealed TC sign, and subsequent biopsy confirmed biliary atresia—the patient ultimately required Kasai hepatoportoenterostomy. 2 This underscores that serial ultrasound examinations are essential when biliary atresia remains in the differential diagnosis despite initial negative findings.