Recent advances regarding endoscopic biliary drainage for unresectable malignant hilar biliary obstruction

Biliary drainage for unresectable malignant hilar biliary obstruction (UMHBO) is still associated with a number of controversies to be resolved. The superiority of bilateral drainage in comparison to unilateral drainage has not been proven obviously yet. However, bilateral drainage is necessary to treat obstructive jaundice in some UMHBO patients, and this may be connected with preservation of the functional liver volume. The partial stent-in-stent (SIS) method and side-by-side (SBS) method developed as bilateral drainage methods. There is no significant difference in the technical or clinical success rates of the SIS and SBS methods. In addition, these methods are comparable in terms of adverse events, patency period, and survival period. On the other hand, reintervention for recurrent biliary obstruction (RBO) after the SBS method seems to be easier in comparison to cases with RBO after the SIS method; however, there is no remarkable difference in the clinical results of these procedures. Endoscopic ultrasound (EUS)-guided biliary drainage also has become an option for patients with UMHBO. Left hepatic drainage using EUS-guided hepaticogastrostomy (EUS-HGS) has become common; however, few studies have reported the results of bridging drainage for the right lobe using the EUS-HGS route or EUS-guided hepaticojejunostomy. A few studies addressed the results of newly designed stents, such as the 6-mm braided metal stent and inside stent. The development of various drainage methods and new devices is necessary for the further advancement of endoscopic biliary drainage for patients with UMHBO, further studies to evaluate those methods and devices are warranted.