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Page 10 of 16 Chandrasekar et al. Mini-invasive Surg 2021;5:33 https://dx.doi.org/10.20517/2574-1225.2021.12

[70]
et al. in their meta-analysis showed the median stent patency duration to be 167.7 days for SEMS while
[71]
only 73.3 days for plastic stents, with lower rates of cholangitis in SEMS. Sangchan et al. in their RCT
demonstrated a survival benefit for patients with SEMS compared to plastic stents but other studies have
shown mixed results. Thus, the consensus is the use of SEMS for MBO, especially for distal strictures. The
role of plastic stents for distal MBO is typically considered in patients with a life expectancy of fewer than 3
months.

Type of SEMS
Biliary SEMS come in diameters of 6, 8 and 10 mm with lengths from 4 to 10 cm. They can be of 3 types:
fully covered (FCSEMS), partially covered (PCSEMS) or uncovered (USEMS). These stents are made from
[72]
various materials and can be present with or without anti-migration valves and anti-reflux mechanisms .
They each have their own set of advantages and disadvantages. Generally, FCSEMS are more expensive and
have higher rates of migration and reflux of duodenal contents, but they are easily removable . They have
[73]
[74]
also demonstrated higher rates of cholecystitis if the stent is placed across the cystic duct . In comparison,
USEMS have higher rates of tissue ingrowth and difficult to remove but have lower rates of migration. Both
have comparable patency rates. The choice of SEMS in patients depends primarily on the level of biliary
obstruction, distal MBO vs. proximal MBO due to hilar strictures, and whether removability may be
important (e.g., indeterminate strictures).

For distal unresectable MBO, FCSEMS or UCSEMS are the primary options. Several studies have been
performed comparing these two stents with conflicting results. Lee et al. in their retrospective study
[75]
showed a higher rate of tissue ingrowth with obstruction in USEMS (76% vs. 9%) but stent migration was
[76]
more common in FCSEMS (36% vs. 2%). In contrast, Conio et al. in their RCT of 158 patients found
[77]
higher rates of stent migration as well as stent occlusion in FCSEMS. Majmudar et al. demonstrated
higher rates of cholecystitis by 15% for FCSEMS when compared to USEMS but another study by Isayama
[73]
et al. showed no statistically significant difference between the two stents for cholecystitis in distal MBO.
Thus, there is no consensus on the ideal type of stent to be used for distal MBO. The choice of stents should
be individualized for every patient, depending on other clinical factors, life expectancy, possible need for
removal and plan for chemoradiation.

For malignant hilar strictures, the choice of stents are either plastic or USEMS. Plastic stents are generally
preferred for palliative stenting to relieve the biliary obstruction. FCSEMS are generally not preferred as
they can cause blockage of the contralateral intrahepatic duct system. Several studies have investigated
[78]
unilateral (left or the right duct system) or bilateral stenting. De Palma et al. in their RCT of 157 patients
with hilar obstruction, comparing unilateral and bilateral stenting, demonstrated superior stent insertion
rates with unilateral stenting (88.6% vs. 76.9%, P = 0.04) and higher complication rates with bilateral stenting
(26.9% vs. 18.9%, P = 0.03) on intention-to-treat analysis. A meta-analysis by Aghaie Meybodi et al. of
[79]
1300 patients with hilar strictures demonstrated comparable efficacy and safety for unilateral and bilateral
stenting. Although in theory, bilateral stenting would make sense in draining more volume of the liver,
studies have not shown the difference in survival, efficacy or complication rates between these two
techniques. The principle of biliary stenting is to aim for drainage of at least 50% of the volume of the liver
as studies have demonstrated a decreased risk of cholangitis and improved survival with it. Obtaining
imaging prior to and after biliary stenting may provide information on the effective liver volume that is
drained.

Radiofrequency ablation
Radiofrequency ablation (RFA) involves the administration of thermal energy to the malignant tumor
causing tissue destruction with necrosis. The indications for the use of RFA are primarily focused on