Occult mucin-producing cholangiocarcinoma in situ: a rare clinical case with difficult tumour staging

BACKGROUND: Mucin-producing cholangiocarcinoma (MPCC) is an uncommon tumour that is clinically characterized by mucin-hypersecretion. Because the initial symptoms of MPCC may be attributed to the viscus mucobilia, the primary tumour mass may potentially be unrecognizable. We report an interesting case of curatively resected occult MPCC in situ. CASE PRESENTATION: A 70-year-old man was referred to our hospital with increased levels of biliary enzymes. Multidetector row computed tomography (MDCT) demonstrated a diffuse dilatation of the entire biliary system without evidence of tumour mass. Additionally, there were numerous variably sized cysts throughout the liver. The cyst of S4 was the largest, followed by that of S1, which connected with the right hepatic duct. Endoscopic retrograde cholangiography showed intrabiliary mucus, predominantly in the left hepatic duct, but failed to show a communication of both cysts with the bile duct. We clinically suspected that minute MPCC was present within the S1 cyst and performed left hepatectomy, caudate lobectomy, and resection of the extrahepatic bile duct. Macroscopically, papillary adenocarcinoma in situ was present in the S1 cyst, and a final diagnosis of MPCC originating from the bile duct of the caudate lobe was made. CONCLUSIONS: For MPCC, in practice, we should consider the possibility that this tumour can be occult. In this complicated setting, demonstrating the communication to the responsible dilated duct is a clue to the diagnosis. Multidirectional MDCT images succeeded in specifically demonstrating this communication, which is insensitive to the presence of excessive mucobilia.