Several investigators have identified characteristic cholangioscopic findings in various biliary-tract diseases (Table 1). The normal bile duct shows a flat surface, with or without shallow pseudodiverticulae, which represents the orifice of the bile duct gland and a fine network of normal thin vessels. In inflammatory diseases, e.g., chronic cholangitis and primary sclerosing cholangitis, irregular surface, scarring, and pseudodiverticulae with or without intradiverticulae are often seen [22]. Dilated tortuous vessels without encasement or fusion of vessels can be seen in immunoglobin G4 (IgG4)-related sclerosing cholangitis due to vascular congestion [22]. On the other hand, irregular papillary or granular lesions, and nodular elevated lesions are typical cholangioscopic findings that raise concern for biliary neoplasia. Friability of the lesions and easy bleeding are often seen with dilated or non-dilated tortuous vessels. In terms of typical neoplastic vessels, so-called “tumor vessels,” either angiogenic or tumorigenic, are partially dilated vessels with encasement and fusion of vessels. We previously reported that the features of vessels were divided into four types: (1) sporadic fine vessels which are frequently seen in normal mucosa, (2) aggregated fine vessels without dilation which are frequently seen in chronic inflammation (Type I), (3) dilated and tortuous vessels without encasement or fusion of vessels (Type II), (4) partially dilated vessels without encasement and fusion of vessels (Type III; Fig. 2, Vessel patterns). Type I vessels are usually benign and Type III are typically malignant lesions. However, in the case of Type II vessels, such a differentiation between benign and malignant lesions poses a diagnostic dilemma given the cholangioscopic similarities .

In a mother–daughter system, therapeutic interventions are limited by the size of the available 1.2-mm working channel. Devices which fit in this narrow-working channel include the 1.9-Fr electrohydraulic lithotripsy probe (Fig. 3) and holumium yttrium aluminum garnet (YAG) laser lithotripsy. On the other hand, in PDCS using ultra-slim endoscopes, which accommodate 5-Fr devices, various therapeutic interventions (Fig. 4) such as therapeutic drug injection, tumor resection , stone extraction, migrated stent removal, argon plasma coagulation (APC), and photodynamic therapy (PDT), are feasible .

Cholangioscopy procedures are performed with the patient in the prone position with intravenous anesthesia (propofol, 0.5 mg/kg) or with conscious sedation (intravenous midazolam, 0.05 mg/kg).

To improve visualization during cholangioscopy, regardless of the type of POCS used, either sterile saline solution or carbon dioxide insufflation has been used. One comparative study revealed that carbon dioxide insufflation provides better imaging and reduces procedure time compared to sterile-saline solution in almost all cases except in biliary protruding lesions [23].