Recent Advances in Pancreato-Biliary Endoscopic Intervention: How to Resolve Unmet Needs in Pancreato-Biliary Diseases Endoscopically

Various procedures are available for pancreato-biliary (PB) endoscopic interventions [...].

stent is placed above the papilla to prevent reflux of duodenal juice and contents, with the aim of reducing the incidence of recurrent biliary obstruction (RBO) and subsequent long time to RBO. This stent was developed by a Japanese endoscopist [12][13][14] but has not been evaluated prospectively or in a comparative study. A prospective single-arm multicenter study evaluated the feasibility of an inside stent [15]. The inside stent showed a long time to RBO in cases of benign biliary stricture (BBS) and superiority to conventional plastic stents in malignant cases. In the Japanese clinical practice guidelines for biliary cancer, plastic stents and self-expandable metallic stents are recommended equally for the management of unresectable hilar cholangiocarcinoma [16]. The difficulty of re-intervention because of an occluded stent is a problem with uncovered self-expandable metal stents (SEMSs), and exchangeability is important for hilar cholangiocarcinoma because of prolonged survival due to effective chemotherapy [17].
Endoscopic management of BBS has changed markedly in the last decade. Endoscopic procedures aim to both relieve symptoms and resolve the stricture [18]. To dilate the BBS, placement of multiple plastic stents and fully covered SEMSs is effective [19,20]. Fully covered SEMSs are effective for BBS via the percutaneous and anastomosis routes, followed by endoscopic ultrasonography (EUS)-guided biliary drainage [21]. Bilioenteric anastomosis stricture hampers approaching the anastomotic site via an endoscope. The percutaneous and transluminal routes are promising but are not ideal for inserting multiple catheters. Fully covered SEMSs are recommended for such cases, despite the lack of an established removal method. Free insertion of stents by various routes and to a variety of locations may be beneficial for both patients and endoscopists [22].
The initial indication for interventional EUS (IV-EUS) was management of peripancreatic fluid collection including pseudocysts and walled-off necrosis [23]. EUS-guided drainage/anastomosis (EUS-D/A) is effective, but infected necrotic tissues and dead space including infected liquid confined in necrotic tissues cannot be drained by simple drainage. Necrosectomy enables retrieval of necrotic tissues and opening of the dead space [24]. Currently, there are many guidelines for the management of walled-off necrosis after severe pancreatitis [25,26]; however, the procedure is inefficient and risky and may be fatal.
EUS-guided rendezvous enables biliary access when conventional cannulation fails [27]. According to the scope position, there are three routes: transgastric, transduodenal short scope position, and transduodenal long scope position [28,29]. Each has its advantages and disadvantages, and no standard strategy has been established. Matsubara et al. proposed a new algorithm for selecting the approach route [30]; the hitch-and-ride technique they developed reduces the difficulty of EUS-guided rendezvous [31].
A stent is key for treatment success and a good prognosis. Transluminal drainage/ anastomosis stents (T-DAS) for IV-EUS required various abilities, insertion, drainage, prevention of leakage and migration. Lee et al. reviewed conventional stents and dedicated T-DASs and described their functions in interventional EUS procedures [32]. Prevention of migration is important for IV-EUS drainage [27]. This fatal complication could be prevented by developing effective T-DASs but also by considering the patient's status. Ochial et al. analyzed risk factors for stent migration in EUS-guided hepaticogastrostomy [33]. From their experience, there is both real migration and imminent migration, and the distance between the liver and gastric wall on computed tomography before the procedure was a risk factor. During the procedure, we aim to shorten this distance, but the gastric wall may return to the original position after treatment. In such cases, we select a >10 cm stent with >5 cm in the stomach [34]. Development of a covered SEMS with effective anchorage is needed for widespread use of EUS-guided hepaticogastrostomy.
After successful EUS-guided drainage/anastomosis, several procedures involving anastomosis may be performed. Endoscopic necrosectomy was reported by Seewald et al. [35]. EUS-D/A can create a route between non-adherent organs, facilitating endoscopic procedures. After EUS-D/A, stone and stricture management by cholangioscopy/pancreatotomy is possible in cases of biliary, gallbladder, and pancreatic drainage [36][37][38][39]. These are transluminal endoscopic procedures or endoscopic procedures through the anastomosis following EUS-D/A. After EUS-guided gallbladder drainage, stones are removed through the matured anastomosis, and cholecystectomy is not necessary.
In conclusion, various endoscopic procedures can be used to ameliorate symptoms. However, there are many unmet needs. Efforts to establish a strategy and develop new methods/devices will enhance the safety and efficacy of the procedure. Funding: This research received no external funding.

Conflicts of Interest:
The authors declare no conflict of interest.