The most important confirmatory test is an ultrasound scan. US confirm gallstones, showing thickening and oedema of the gallbladder wall and localise the tender spot to the gallbladder itself. It can also exclude dilatation of the common bile duct and other pathology, such as liver masses.
The triangular cord sign is a triangular or tubular echogenic cord of fibrous tissue seen in the porta hepatis at ultrasonography and is relatively specific in the diagnosis of biliary atresia This sign is useful in the evaluation of infants with cholestatic jaundice, helping for the differential diagnosis of biliary atresia from neonatal hepatitis. It is defined as more than 4 mm thickness of the echogenic anterior wall of the right portal vein (EARPV) . http://radiopaedia.org/article