An extremely rare case of symptomatic right hepatic duct diverticulum located outside the liver.

Symptomatic hepatic duct diverticulum located outside the liver is extremely rare, with only one reported case. We encountered this anomaly and present our experience, focusing on surgical management. A 17-year-old-girl was referred to our institute because of recurrent right upper quadrant pain. At presentation, serum amylase, lipase, bilirubin, and transaminases were normal. White blood cell count and C-reactive protein were slightly raised. Ultrasonography and magnetic resonance cholangiopancreatography (MRCP) revealed a diverticulum-like lesion on the right side of the bile duct system appearing to overlap the gallbladder. The provisional diagnosis was type II choledochal cyst. Pancreaticobiliary malunion (PBMU) could not be confirmed on MRCP. The origin of the lesion could not be identified initially at laparotomy, but after repeated intraoperative cholangiography (IC) studies, the lesion was found to originate from a normal-sized right hepatic duct via a narrow duct. It was relatively easy to ligate the narrow duct and treat the lesion smoothly. IC also showed that the common bile duct was not dilated and that PBMU was absent. Histopathology showed the lesion to be a diverticulum of the bile duct epithelium. This is only the second report of a symptomatic hepatic duct diverticulum located outside the liver. Based on our experience, IC is particularly useful for the complete understanding of anomalous hepatobiliary duct anatomy and for planning surgical treatment.