Equipment and techniques

POCS was initially described in 1976. PTCS was also developed in the 1970s. The adoption of these procedures has been slowed in part by technological limitations of the cholangioscopes. One of the first reports demonstrated a fiberscope of 8.8 mm diameter, which was inserted perorally into the biliary system after endoscopic sphincterotomy without the need of a second guiding scope. In the following years the idea of guiding a small-caliber “baby” cholangioscope through the channel of a dedicated larger channel “mother” duodenoscope into the common bile duct (CBD) gained wide acceptance. This “mother-baby” system is operated by 2 experienced endoscopists. The conventional fiberoptic scopes used in the mother-baby system have a distal diameter of 4.5 mm. The scopes have one instrumental channel and the tip deflection is limited to one plane (up-down) of approximately 90° without lateral deflection. The baby scopes are fragile and their optic fibers are prone to break easily from pressure applied with the elevator of the duodenoscope. These scopes require a dedicated light source, image processor, and water-air pump. Finally the baby scope image is projected onto a separate video monitor. Two endoscopists are required and a prior sphincterotomy or balloon sphincteroplasty is usually necessary to insert the baby scope into the CBD. To facilitate ductal intubation, administration of agents that relax the sphincter of Oddi, such as hyoscines, glucagon, and isosorbide dinitrate, have been reported to be helpful. Inserting the baby scope over a guidewire into the duct reduces the need for elevator use and risk of scope damage. Once the scope is advanced to the target location, the guidewire should be removed to permit use of the accessory channel for irrigation and introduction of devices. Several miniscopes have been developed with reduced diameters ranging from 2 to 3.5 mm, allowing insertion thorough conventional therapeutic duodenoscopes and their delivery into even small bile ducts. If the outer diameter is less than 2.5 mm, access without prior sphincterotomy is possible. A fine-caliber flexible miniscope created by Soda and colleagues allowed access to the CBD without sphincterotomy, due to its external diameter of 2.09 mm including, unlike many other miniscopes, a central working channel of 0.72 mm. Similarly, Sander and Poesl have developed a less fragile, steerable new miniscope for peroral cholangioscopy with 2 different degrees of stiffness and 2 channels: a 0.4-mm (1.2F) irrigation channel and a 1.2-mm (3.6F) working channel through which a probe for EHL and a stone extraction basket can be passed. Slightly larger miniscopes with bidirectional angulation systems and instrumental channels were developed by several companies. Despite these advances, POCS has remained a very cumbersome and time-consuming procedure that has not reached the expected popularity because it requires 2 experienced endoscopists to perform and has a small spectrum of possible applications. However, image quality and size have been significantly improved by the implementation of video cholangioscopes that use high-resolution video chips ( Fig. 1 ). The charge-coupled device (CCD) video chip is mounted in the distal tip of the scope and provides a 100° forward direction field of view. Disadvantages of these scopes were the lack of an accessory channel for interventional applications or a very limited working channel of only 0.5 mm. A newer “hybrid” video baby scope integrates a 1.2-mm accessory channel into a scope of 2.8 mm external diameter. The CCD unit is located in the control section, which protects the video chip from the usual scope trauma and may improve the durability of the scope. The image quality of glass fiber–based hybrid cholangioscopes with the CCD unit located in the control section is inferior to those with the CCD unit located in the tip of the scope. However, the video cholangioscope is still fragile and is not yet widely available. Despite technological advances in the design and maneuverability of miniature endoscopes and their accessories, few technical improvements have been made regarding the main concept of the mother-baby system. Limited tip deflection and the lack of optimal irrigation systems compromise visibility, requiring extra time and effort to complete the procedure. An additional limitation is the small caliber (range 0.5–1.2 mm) of the working channel that allows the use of only small biopsy forceps, which are able to obtain very small and often inadequate tissue samples. Table 1 summarizes and compares the currently available cholangioscopic technologies.

Mother-and-baby cholangioscopy. The tube of the video cholangioscope is inserted into the working channel of a therapeutic duodenoscope, which is attached to a special belt (“scope dock device”) of the endoscopist to facilitate the procedure.

The search for a less cumbersome technique has led to the application of ultraslim gastroscopes to perform direct visualization and treatment of biliary disease. With external diameters of 5 to 6 mm, these instruments are only suitable for examination of the CBD after a sphincterotomy. An ERCP is performed first to place a 0.035-in diameter super-stiff guidewire as far into the bile duct as possible. After sphincterotomy the duodenoscope is cautiously removed and the ultraslim upper endoscope is then inserted over the guidewire, under fluoroscopic and endoscopic control, into the duodenum and across the ampulla of Vater into the CBD. Even with the guidewire in place, intubation and deep advancement of the endoscope into the bile duct can be limited by vector forces that tend to advance the scope along the axis of the duodenum, as well as looping the scope in the stomach. Loop formation can be reduced by use of an overtube, which can be mounted on the gastroscope, to facilitate this part of the procedure. Although the currently available overtube is too large in diameter for an ultraslim endoscope, making it difficult to manipulate both the overtube and the endoscope, it has been frequently adopted among Japanese and Korean endoscopists during POCS with ultraslim upper endoscopes. A pilot study evaluated the feasibility of POCS with an ultraslim endoscope and an intraductal balloon that can be anchored in a branch of an intrahepatic duct (IHD) with the similar procedure using a guidewire. A specialized 5F balloon catheter is required to fit the 2.0-mm working channel of the endoscope. After anchoring the intraductal balloon within a biliary branch, the endoscope can be advanced over the balloon catheter into the proximal biliary system. The investigators reported a success rate of 95.2% intraductal balloon-guided POCS compared with 45.5% for wire-guided POCS, and described no difficulties in negotiating through the hilum into the right or left ductal system once they were in the CBD. In addition, repeated advancement and withdrawal of the scope through the firmly anchored balloon catheter was possible. Nevertheless, anchoring the balloon within a branch of the IHD is not possible in some patients, and the intraductal balloon should be withdrawn from the scope to perform tissue sampling or therapeutic intervention, which can create technical difficulties in maintaining the desired endoscope position. An ultrathin balloon catheter was recently developed for placement over a guidewire by means of standard ERCP. After inflation and anchoring in the proximal biliary tree the balloon can be sealed before detachment of the handle. This technique allows removal of the duodenoscope and backloading of an ultraslim gastroscope for subsequent insertion over the anchored balloon catheter. The catheter can then be removed for insertion of accessories such as biopsy forceps ( Fig. 2 A–D). This promising new method is currently under clinical evaluation.

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