What are the contraindications for Lumen-Apposing Metal Stent (LAMS) placement in a pancreatic collection in terms of vascularity, distance from the stomach wall, and collection wall thickness?

Contraindications for LAMS Placement in Pancreatic Collections

For safe LAMS placement in pancreatic collections, the distance between the enteral puncture site and collection should be less than 10 mm, the collection wall should be adequately thick (at least walled-off), and significant vascularity in the puncture tract should be avoided to prevent bleeding complications. 1, 2

Vascularity Considerations

• Major contraindication: Presence of intervening vessels in the puncture tract between the gastrointestinal wall and the collection
• Assessment method: Pre-procedural dynamic CT with contrast to identify vascular structures
• Risk: Significant vascularity increases risk of bleeding, which can occur in up to 4-8% of cases 1, 3
• Mitigation: Color Doppler should be used during the procedure to identify and avoid blood vessels in the puncture path

Distance from Stomach/Duodenal Wall

• Maximum safe distance: Less than 10 mm between the enteral wall and collection 1
• Extended reach option: A novel 15-mm-long LAMS can be used for collections located 10-14 mm from the luminal wall with 97% technical and clinical success rates 2
• Risk of greater distance: Increased risk of stent misdeployment, bile leakage, and peritonitis
• Alternative approach: For collections >10-14 mm from the wall, consider using the over-the-wire technique rather than direct puncture to maintain access in case of stent misdeployment 1

Collection Wall Thickness

• Minimum requirement: Collection must be adequately walled-off with a mature capsule
• Timing: Typically requires 4+ weeks from onset of pancreatitis for adequate wall formation
• Risk of premature drainage: Immature collections with thin walls increase risk of leakage, peritonitis, and procedural failure
• Assessment: Pre-procedural imaging (CT/MRI) to confirm adequate wall formation

Additional Safety Considerations

• Coaxial plastic stent placement: Placing double-pigtail plastic stents through LAMS is recommended to:

  • Reduce risk of stent obstruction (OR 0.59, p=0.004)
  • Decrease infection rates (OR 0.55, p=0.001)
  • Potentially reduce bleeding from LAMS eroding into collapsed cavity walls 4, 5

• Stent removal timing: If using metal stents for EUS-guided drainage, they should be removed within 4 weeks to avoid food impaction and recurrence of complications 1

• Multidisciplinary support: Centers performing LAMS placement should have support from interventional radiologists, surgeons, and anesthesiologists to manage potential complications 1, 3

Procedural Algorithm

1. Pre-procedure assessment:

   • Confirm collection is walled-off (typically >4 weeks from onset)
   • Verify distance from GI tract wall is <10 mm (or <14 mm if using 15-mm LAMS)
   • Perform contrast-enhanced CT to rule out intervening vessels

2. During procedure:

   • Use color Doppler to confirm absence of vessels in puncture path
   • For collections with distance >10 mm, use over-the-wire technique rather than direct puncture
   • Consider placement of double-pigtail plastic stent through LAMS to reduce complications

3. Post-procedure management:

   • Plan for stent removal within 4 weeks
   • Monitor for bleeding, infection, and stent migration

Common Pitfalls and Caveats

• Bleeding risk: Higher with LAMS compared to plastic stents, especially with delayed bleeding from pseudoaneurysm formation
• Buried stent syndrome: Can occur with prolonged stent placement
• Cost considerations: LAMS is more expensive than plastic stents without significant differences in outcomes in some studies 1
• Technical expertise: Procedure should be performed by endoscopists with adequate experience in therapeutic EUS

By adhering to these guidelines regarding vascularity, distance, and wall thickness, the safety and efficacy of LAMS placement for pancreatic collections can be optimized.