Pancreato‐hepatobiliary endoscopy: Cholangioscopy

Cholangioscopy has both been used as a diagnostic, as well as a therapeutic procedure. The fiber-optic cholangioscope, developed in the 1970s, had been used in post-operative cholangioscopy (POC), percutaneous transhepatic cholangioscopy (PTCS), and peroral cholangioscopy (POCS). Cholangioscopes used in POCS (mother–baby cholangioscopes) are composed of a mother duodenoscope and a baby cholangioscope. The cholangioscope is advanced through the working channel of the duodenoscope over a guidewire. In direct POCS, an ultra-thin endoscope is directly advanced into the bile duct. Single-operator cholangioscopy using SpyGlass is one of mother–baby systems. Direct POCS is classified into single-operator cholangioscopy. Possible indications for cholangioscopy of the bile duct include direct visual assessment, tissue sampling, and therapeutic interventions. In 1974, Yamakawa et al.1 reported that POC, being a minimally invasive technique, is useful in the treatment of biliary stones. POC is well-suited for patients in which full clearance of calculi is not achieved during surgery, especially in those with hepatolithiasis. It has a high rate of biliary calculi removal and a low rate of recurrence and complications. In the same year, Takada et al.2 first described PTCS, which has been the most widely used modality for the diagnosis and treatment of biliary diseases. PTCS plays an important role in the pre-operative diagnosis of biliary malignancy, as well as in the treatment of difficult stones, including hepatolithiasis. Nimura et al.3 described irregularly dilated tortuous vessels as a characteristic cholangioscopic finding that indicates the presence of a malignancy. They also noted that papillary or infiltrative cholangiocarcinoma spreads superficially along the bile duct mucosa. The evaluation of longitudinal tumor extension using PTCS provides a clue for resectability assessment. Hepatolithiasis is often associated with bile duct strictures that lead to the development of recurrent cholangitis and/or cholangiocarcinoma. Although hepatectomy is ideal, surgery alone is often inadequate for the complete removal of intrahepatic stones that exist in bilateral lobes. In addition to surgery, PTCS is an ideal treatment modality for hepatolithiasis. In the 1970s, POCS was introduced as a minimally invasive procedure for the evaluation and treatment of biliary diseases.4 In 1976, Nakajima et al.5 described a prototype fiber-optic mother–baby scope system, which has undergone advancements, and has been in wide-spread clinical use as a standard POCS. A seemingly benign biliary stricture may actually be malignant, and strictures thought to be malignant may be benign. Intraductal tumors may mimic large stones, and immobile stones may imitate polypoid tumors. Indeterminate biliary strictures are of utmost clinical concern because brush cytology and biopsies with endoscopic retrograde cholangiopancreatography (ERCP) are limited by the relatively low sensitivity. In a single-center Japanese study, POCS improved the diagnostic accuracy for undetermined bile duct strictures from 78.1% to 93.4%, and that for filling defect to 100%, compared to endoscopic retrograde cholangiography (ERC) with biopsy.6 In this study, malignant strictures with irregularly torturous vessels (Fig. 1), easy oozing, or irregular surface were observed by visual appraisal. In 2004 the video POCS system was introduced with high-definition images and the incorporation of optical chromoendoscopy (narrow band imaging), which can be useful in the evaluation of bile duct or pancreatic duct mucosal lesions.7 Kawakami et al.8 reported that pre-operative video POCS with biopsy provided a more accurate diagnosis of the extent of intraepithelial tumors in biliary cancer than did ERC alone. In 2013, a prospective multicenter study showed that video POCS improved the accuracy of the diagnosis of indeterminate biliary lesions from 85.7% to 92.1%, and that of cancerous extension from 73.5% to 83.7%.9 Once a cholangioscope could advance beyond the biliary strictures, video peroral cholangioscopy was effective in the pre-operative assessment of longitudinal extension of cholangiocarcinoma. Immunoglobulin G4 (IgG4)-related disease is a systematic sclerosing disorder characterized by fibrotic lesions in the form of a mass-like lesion that contains dense IgG4-positive lymphoplasmacytic infiltrates. Since it mimics tumors on images, IgG4-sclerosing cholangitis (IgG4-SC) may often be misdiagnosed as pancreatobiliary cancer.6 Itoi et al.10 were the first to describe the role of cholangioscopy in patients with IgG4-SC, with dilated tortuous vessels and an absence of partially enlarged vessels being the most frequent findings. Although the incidence of dilated vessels was significantly higher in patients with IgG4-SC than that in those with cholangiocarcinoma, partially enlarged vessels may be a specific finding in cholangiocarcinoma. Primary sclerosing cholangitis (PSC) is known to be characterized by indeterminate bile duct strictures as well as IgG4-SC. Cholangioscopic findings of PSC benign stricture are scarring and pseudodiverticula; which were found significantly more often in PSC than in IgG4-SC. However, a significant proportion of patients with PSC developed dominant bile duct strictures, which suggests a possible sign of malignancy. Early detection of cholangiocarcinoma in patients with PSC was still challenging. Intraductal papillary neoplasm of the bile duct (IPNB) is a rare variant of bile duct tumors, characterized by prominent papillary proliferation (Fig. 2), with or without mucin secretion. The World Health Organization Classification of Tumors of the Digestive System in 2010 described IPNB as one of the precancerous, pre-infiltrating lesions of the bile duct. ERC is useful for the detection of mucobilia; however, it fails to locate tumors in the dilated bile duct filled with mucin. POCS can approach the bile duct directly and can confirm the extent of the tumor.11 When endoscopists observe mucobilia or a mucin-filled papillary orifice, the presence of IPNB must be considered, and POCS should be performed to confirm the diagnosis. In patients with excessive mucin, targeted biopsies under cholangioscopy are intractable because during the procedure, sufficient irrigation to keep the cholangioscopic view clear is difficult in the presence of thick mucin. On the contrary, IPNB without mucin secretion can be visualized clearly by POCS, and targeted biopsies are preferred for confirming pathological evidence. Over 85% of bile duct stones can be managed with standard ERCP techniques, including mechanical lithotripsy (ML). ML-resistant bile duct stones, due to large stones, impacted stones, or broken traction wires on the basket, are called "difficult bile duct stones". POCS-directed lithotripsy (PC-directed lithotripsy), using electrohydraulic lithotripsy or laser lithotripsy, is effective in the management of difficult bile duct stones.12 ML is ineffective in the management of Mirizzi syndrome (MS), which is classified into the following two types: type I, in which the acute form is characterized by external compression of the adjacent common hepatic duct; and type II, in which a pressure necrosis of the common bile duct results in a cholecystocholedochal fistula (Fig. 3). POCS can access impacted stones via the fistula. In a large retrospective series, the overall stone removal by PC-directed lithotripsy was successful in 117 (95.9%) of 122 patients with difficult bile duct stones (MS type I, 3; MS type II, 50; impacted stone, 50; and large stone, 19). Of the 50 patients who had MS type II, 48 (96%) were successfully treated. Three patients with MS type I underwent open cholecystectomy. Long-term follow-up data are available; bile duct stone recurrence was observed in 18 patients (16.1%). The multivariate analysis showed that dilated bile duct diameter (≥20 mm) is the only risk factor for stone recurrence after PC-directed lithotripsy. Currently, similar to mother–baby systems, single-operator POCS systems are available and overcome some of the limitations of the video POCS systems; the single-operator design, continuous irrigation equipment, as well as the four-way tip deflection have improved its usability. The effectiveness of PC-directed lithotripsy in the management of intrahepatic stones is limited by the inability to advance the cholangioscope through the narrow hepatic duct and bile duct stricture. Okugawa et al.13 reported complete intrahepatic stone clearance rate of 64% (23/36) using PC-directed lithotripsy. Despite the fact that the complete clearance rate was lower than that of PTCS lithotripsy, the cumulative recurrence rate was relatively low (21.7% at 164 months) after the procedure, which compares favorably with that for PTCS lithotripsy. Urakami et al.14 were the first to report direct POCS using a forward viewing endoscope. Compared to the standard POCS (mother–baby system), direct POCS provides higher quality endoscopic images as well as relatively a larger working channel, which can be used for tissue sampling and interventional procedures. The major obstacle in direct POCS is the acute angle between the duodenum and the bile duct. Although passing an intraductal balloon catheter through the scope can permit access of the ultra-thin endoscope to the bile duct, anchoring of the intraductal balloon catheter is not always successful. Moreover, an ultra-thin scope which is thicker than a cholangioscope is more difficult to cannulate into the non-dilated bile duct than is a baby scope. The commercially available ultra-thin scope is not designed for use as a cholangioscope. A direct cholangioscope prototype has been developed for free-hand insertion into the bile duct.15 Hence, the mother–baby scope system is more preferrable for the examination of bile duct strictures than is the direct POCS system, due to the better stability of the cholangioscope. Peroral cholangioscopy is a relatively safe procedure; the most common complication being cholangitis. Continuous saline irrigation to maintain a good view often causes intraductal pressure elevation, resulting in acute cholangitis. Air embolism is a rare but possible fatal complication, even when carbon dioxide is used. Cholangioscopy has developed significantly since the advent of the early fiber-optic mother–baby systems, and many Japanese endoscopists have contributed greatly to its clinical utility. The future of cholangioscopy will depend on further cutting-edge improvements in high-quality images, ease of use, cost effectiveness, and the development of various accessories. Author declares no conflict of interest for this article. None.