Department of Gastroenterology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Dig Endosc. 2013 May;25 Suppl 2:71-4. doi: 10.1111/den.12078.
Self-expandable metallic stents (SEMS) are a widely accepted biliary endoprosthesis for patients with unresectable malignant distal biliary obstruction. There are two types of SEMS: covered and uncovered. Uncovered SEMS (UCSEMS) embed into the biliary wall due to their mesh structure and self-expandability, and are resistant to migration. However, the disadvantage of UCSEMS is occlusion due to tumor ingrowth (TI) via the stent mesh, and TI is the main cause of UCSEMS occlusion. To overcome this, covered SEMS (CSEMS) were developed and showed longer patency than UCSEMS. However, migration due to the non-embedded stent body is the main cause of CSEMS dysfunction. There are some randomized studies comparing CSEMS and UCSEMS; however, the results are different according to each study. From one meta-analysis, CSEMS showed longer patency than UCSEMS. A literature review revealed that covered SEMS showed longer patency than UCSEMS. Some studies cannot clearly demonstrate the superiority of CSEMS, as the CSEMS used did not prevent TI or migration. Mechanical properties of SEMS may influence the occurrence of complications. A recent clinical study comparing the Covered Wallstent and the Covered WallFlex revealed superiority of the WallFlex for the prevention of migration. Reducing the axial force and increasing the radial force may lead to good results. Migration of CSEMS should be prevented by taking into consideration the mechanical properties of stents and development of anti-migration systems.
自膨式金属支架（SEMS）是一种广泛应用于不可切除的恶性远端胆道梗阻患者的胆道内支架。SEMS 有两种类型：覆膜和非覆膜。由于其网状结构和自膨性，非覆膜 SEMS（UCSEMS）会嵌入胆道壁，不易发生迁移。然而，UCSEMS 的缺点是肿瘤通过支架网眼向内生长（TI）导致支架阻塞，TI 是 UCSEMS 阻塞的主要原因。为了克服这一问题，开发了覆膜 SEMS（CSEMS），其通畅时间长于 UCSEMS。然而，由于支架体未嵌入，导致迁移是 CSEMS 功能障碍的主要原因。有一些比较 CSEMS 和 UCSEMS 的随机研究；然而，根据每项研究的结果不同。一项荟萃分析显示，CSEMS 的通畅时间长于 UCSEMS。文献回顾显示，覆膜 SEMS 的通畅时间长于 UCSEMS。一些研究不能清楚地证明 CSEMS 的优越性，因为使用的 CSEMS 并不能预防 TI 或迁移。SEMS 的机械性能可能会影响并发症的发生。最近一项比较 Covered Wallstent 和 Covered WallFlex 的临床研究显示，WallFlex 具有更好的预防迁移的效果。减少轴向力和增加径向力可能会带来良好的效果。通过考虑支架的机械性能和开发抗迁移系统，可以预防 CSEMS 的迁移。
