Key imaging features for differentiating cystic biliary atresia from choledochal cyst: prenatal ultrasonography and postnatal ultrasonography and MRI

Abstract

Purpose: This study compared clinical and radiologic differences between cystic biliary atresia (cBA) and choledochal cyst (CC) type Ia/b.

Methods: Infants (≤12 months old) who were diagnosed with cBA or CC type Ia/b from 2005 to 2019 were retrospectively reviewed. Imaging features on preoperative ultrasonography (US) and magnetic resonance imaging (MRI) were compared between the cBA and CC groups. Logistic regression and area under the receiver operating characteristic curve (AUC) analyses were performed for the diagnosis of cBA. Changes in cyst size were also evaluated when prenatal US exams were available.

Results: Ten patients (5.5% of biliary atresia cases) with cBA (median age, 48 days) and 11 infants with CC type Ia/b (Ia:Ib=10:1; median age, 20 days) were included. Triangular cord thickness on US (cutoff, 4 mm) showed 100% sensitivity and 90.9% specificity (AUC, 0.964; 95% confidence interval [CI], 0.779 to 1.000) and cyst size on MRI (cutoff, 2.2 cm) had 70% sensitivity and 100% specificity (AUC, 0.900; 95% CI, 0.690 to 0.987) for diagnosing cBA. Gallbladder mucosal irregularity on US and an invisible distal common bile duct on MRI were only seen in the cBA group (10 of 10). Only the CC group showed prenatal cysts exceeding 1 cm with postnatal enlargement.

Conclusion: Small cyst size (<1 cm) on prenatal US, triangular cord thickening (≥4 mm) and gallbladder mucosal irregularity on postnatal US, and small cyst size (≤2.2 cm) and an invisible distal common bile duct on MRI can discriminate cBA from CC type Ia/b in infancy.

Keywords: Biliary atresia; Choledochal cyst; Magnetic resonance imaging; Neonatal jaundice; Ultrasonography.

Fig. 1.. A girl with cystic biliary atresia.

A. Prenatal ultrasonography (US) at a gestational age of 35 weeks shows a 0.6-cm cyst around the hepatic hilum. B-D. Abdominal US on the second day after birth shows the cyst (0.7 cm) at the hepatic hilum (B), increased periportal echo with triangular cord thickness (double arrow) of 4.8 mm (C), and mucosal irregularity (arrows) of the elongated gallbladder (GB) (D). E-G. Preoperative abdominal magnetic resonance imaging also demonstrates a hepatic hilar cyst (0.7 cm, arrow) on a T2-weighted axial image (E), periportal thickening with a triangular cord thickness (double arrow) of 4.0 mm on a T1-weighted axial image (F), and no visible distal common bile duct (CBD) on three-dimensional magnetic resonance cholangiopancreatography (G). H. Intraoperative cholangiography confirmed an elongated GB with mucosal irregularity (arrows) connected with the cystic lesion (star) in the proximal CBD, an invisible distal CBD, and contrast leakage at the hepatic hilar area without visible normal bile duct branches. She was confirmed to have cystic biliary atresia and underwent the Kasai operation.

Fig. 2.. A boy with choledochal cyst type Ia.

A. Prenatal ultrasonography (US) at a gestational age of 31 weeks shows a hepatic hilar cystic lesion (2.0 cm) and gallbladder (GB). B, C. Postnatal abdominal US also shows the cystic lesion (about 2.6 cm) at the hepatic hilar area with internal sludge, a grossly normal GB (B), and no remarkable periportal echo with a triangular cord thickness (double arrow) of 1.9 mm (C). D, E. T1-weighted axial magnetic resonance images demonstrates the same findings of the cyst (3.4 cm) with internal sludge (D) and periportal signal change with a triangular cord thickness (double arrow) of 3.9 mm (E). F. Magnetic resonance cholangiopancreatography shows patent distal common bile duct (arrow). The cystic lesion was confirmed as a choledochal cyst based on pathology findings.

Fig. 3.. Changes in cyst size from prenatal to postnatal imaging studies.

This spaghetti plot demonstrates changes in cyst size from initial prenatal ultrasonography (US), postnatal preoperative US, and magnetic resonance imaging (MRI) in the order of the routine clinical examinations. The numbers in the graph denote the cyst size. Patient number 1 was a case of cystic biliary atresia and the other four patients had choledochal cyst type Ia. The cyst size was smaller than 1 cm and stable during follow-up in the cystic biliary atresia case, but was larger than 1 cm and showed a growth trend in all cases of choledochal cyst.

Fig. 4.. Comparison of diagnostic performance between ultrasonography (US) and magnetic resonance imaging (MRI) parameters.

Receiver operating characteristic curves of triangular cord thickness (TCT) and cyst size on US and MRI show similar areas under the curve (AUC). The AUC is 0.964 (95% confidence interval [CI], 0.779 to 1.000) for US TCT, 0.886 (95% CI, 0.673 to 0.982) for US cyst size, 0.936 (95% CI, 0.739 to 0.996) for MRI TCT, and 0.900 (95% CI, 0.690 to 0.987) for MRI cyst size, without statistically significant difference (P>0.05).