A lumen-apposing metal stent (LAMS) represents a significant advancement in gastrointestinal endoscopy, designed to create a stable, direct connection between two internal body cavities. This innovative device facilitates drainage of fluid collections and allows for therapeutic interventions that were previously more challenging or required more invasive surgical approaches. LAMS technology has transformed the management of various conditions by offering a minimally invasive alternative.
Understanding Lumen-Apposing Metal Stents
A LAMS features a unique dumbbell or saddle-shaped design with wide, flared ends, which securely anchors the stent and prevents migration. This design creates a broad, open channel between the two anatomical spaces it connects, such as a fluid-filled cyst and the digestive tract. Unlike narrower traditional stents prone to migration or occlusion, the larger lumen of a LAMS allows for more efficient drainage of both fluid and solid debris.
These stents are made from braided nitinol, a self-expanding metal alloy, and are fully covered with a silicone membrane. The silicone covering prevents tissue growth into the stent, minimizes the risk of leakage, and aids removal.
LAMS are available in various sizes, with diameters ranging from 6 mm to 20 mm, and lengths between the flanges around 10 mm. Some modern LAMS incorporate an electrocautery tip, enabling direct and streamlined deployment without additional tools.
Medical Conditions Treated with LAMS Stents
LAMS are primarily used for draining pancreatic fluid collections (PFCs), particularly pancreatic pseudocysts and walled-off necrosis (WON). Pancreatic pseudocysts are fluid-filled sacs that can develop after acute or chronic pancreatitis, while WON involves a collection of both fluid and solid necrotic tissue. These conditions often cause symptoms like abdominal pain, nausea, vomiting, or may lead to complications such as infection or obstruction.
The wide lumen of LAMS facilitates effective drainage of thick fluid and necrotic debris. For WON, it permits direct endoscopic necrosectomy, the removal of dead tissue. This stable, wide drainage pathway makes LAMS a preferred endoscopic approach over traditional surgical or percutaneous methods due to comparable success rates, lower morbidity, and reduced costs.
Beyond PFCs, LAMS also drain gallbladders in patients unsuitable for surgery. They also create gastrointestinal bypasses for gastric outlet obstruction or surgically altered anatomy.
The LAMS Stent Placement Procedure
The placement of a LAMS is a minimally invasive endoscopic procedure, performed under sedation or general anesthesia. The process uses endoscopic ultrasound (EUS) guidance, which provides real-time imaging to identify the target fluid collection or anatomical space. EUS allows the physician to visualize the area, measure the distance between the target collection and the digestive tract wall, and identify any blood vessels to be avoided during the puncture.
Once the optimal site is identified, the EUS endoscope guides the LAMS delivery system. For cautery-enhanced LAMS, the device can directly puncture the wall of the digestive tract and enter the fluid collection or target lumen. The stent is then deployed, with one flange expanding within the collection and the other in the digestive tract, creating a stable connection. This single-step deployment with cautery-tipped LAMS streamlines the procedure, reducing overall procedure time compared to older, multi-step methods.
After LAMS Stent Placement
Following LAMS placement, patients are monitored for a short period to ensure stability and assess for any immediate complications. The stent’s presence allows for continuous drainage of the fluid collection into the digestive tract, leading to symptom relief and resolution of the collection. Follow-up care may involve repeat imaging, such as CT scans, within 3-4 weeks, to assess the resolution of the fluid collection.
LAMS are safe and effective, but complications can occur. These include stent migration, bleeding (immediate or delayed), and infection. Buried stent syndrome occurs when surrounding tissue grows over the stent’s flange, making removal challenging. Stent occlusion, or blockage, can also hinder drainage.
When the fluid collection has resolved, after several weeks to a few months, the LAMS is removed endoscopically. The timing of removal is carefully considered, as prolonged placement has been associated with an increased risk of adverse events like delayed bleeding or buried stent syndrome.