Triangular cord sign | Radiology Signs

Answer:

The triangular cord sign is a triangular or tubular echogenic focus in the porta hepatis, lying immediately anterior to the portal vein bifurcation, representing the fibrous remnant of the obliterated extrahepatic bile duct. It is the key sonographic sign of biliary atresia. It is measured as the thickness of the echogenic anterior wall of the right portal vein on a longitudinal scan, with a threshold above 4 mm taken as abnormal; meta-analyses give a pooled sensitivity of roughly 74-85% with specificity around 97%. It is assessed together with the other features of the disease: the gallbladder ghost triad (length under 19 mm, an indistinct wall without a complete mucosal lining, and an irregular or lobular contour), absent gallbladder, and hepatic subcapsular flow on colour Doppler. Combining features outperforms any single marker. A normal-appearing scan does not exclude biliary atresia, and definitive diagnosis rests on intraoperative cholangiography, so a suspicious study in a jaundiced infant should not delay surgical referral.

Why is it called so?

The echogenic fibrous remnant seen in cross-section forms a triangular or cord-like density at the porta hepatis.

Pathophysiology

Biliary atresia is a progressive inflammatory and fibro-obliterative cholangiopathy of the extrahepatic ducts. The lumen is destroyed and replaced by dense fibrous tissue, which persists as a solid cone of scar at the porta hepatis where the ducts once bifurcated. Fibrous tissue is markedly more echogenic than the adjacent portal venous wall and hepatic parenchyma, so the remnant is rendered as a bright triangular or tubular focus sitting on the anterior surface of the right portal vein. The same obliterative process explains the atretic, non-contractile gallbladder and, through arterial proliferation in the fibrotic portal tracts, the subcapsular flow.

Alternative names: TC sign, triangular cord thickness, echogenic anterior wall of the right portal vein

Other associated named signs: Gallbladder ghost triad, hepatic subcapsular flow sign, and the central dot sign of Caroli disease as a contrasting porta hepatis finding

References

1. Kotb MA, Sheba M, El Koofy N, Mansour S, El Karaksy HM, Dessouki NM, et al. Post-portoenterostomy triangular cord sign prognostic value in biliary atresia: a prospective study. Br J Radiol. 2005;78(934):884-7. PMID: 16177009.