Carcinoma in situ of the perihilar bile duct diagnosed by peroral cholangioscopy.

It is rare for cholangiocarcinoma to be diagnosed as carcinoma in situ. Iwano and colleagues present a case in which stone formation in the hilar region contributed to the diagnosis. In such case, it is important to note minor changes on cholangiography and consider a detailed examination such as peroral cholangioscopy.