Peripancreatic fluid collections (PFCs) have been defined as circumscribed collections around the pancreas. These are known to develop as a result of peripancreatic inflammation and rupture of pancreatic side ducts following acute or chronic pancreatitis, trauma, and surgery [1]. Although most fluid collections without symptoms do not require specific management due to spontaneous resolution, surgical or non-surgical intervention may be required if the size of the cyst increases or accompanying symptoms are present [1-3]. Among several management options, including surgical, percutaneous, and endoscopic approaches, endoscopic ultrasound (EUS)-guided transmural drainage has been steadily increasing in popularity, and has become a standard procedure for the treatment of PFCs as a result of increasing expertise in the therapeutic use of EUS [2].

Traditionally, EUS-guided drainage of PFCs has been performed with EUS-guided cystic wall puncture followed by guidewire insertion, tract dilation, and placement of a plastic stent (PS) under fluoroscopic guidance. Although PS with a double-pigtail design diminishes the risk of migration, there are limitations associated with PS use. These include frequent occlusions due to the small stent diameter, a condition that requires multiple stent placement and multiple revisions to achieve resolution [1,2,4-6]. Recently, a fully-covered self-expandable metal stent (FCSEMS) was used to facilitate PFC drainage owing to a larger lumen diameter. However, FCSEMS is dedicated to draining the biliary or pancreatic duct and does not have antimigratory features, which requires placement of an additional PS.

A lumen-apposing metal stent (LAMS) with a biflanged wide-lumen design was introduced specifically for PFC drainage, and the preliminary data appear to be promising. As the name suggests, a LAMS approximates the wall of the fluid collection to the wall of the stomach or duodenum within a short distance; thus, it may reduce stent migration and serve as a conduit for direct endoscopic necrosectomy. Previous studies have shown lower rates of stent occlusion, stent migration, and perforation, and variable rates of bleeding with LAMS compared to that with PS [1,2,7]. Although the LAMS is a dedicated device for PFC drainage and has technical advantages over PS, there are few data comparing clinical outcomes associated with PS and LAMS. The purpose of our study was to compare the clinical outcomes in patients with PFCs who were treated with EUS-guided transmural drainage using PS or LAMS through a retrospective analysis.

EUS-guided drainage for PFCs has been increasingly used as a minimally invasive procedure and is performed as an effective alternative to surgical treatment in many centers. Previous studies have shown similar success rates with meaningful advantages in comparison to percutaneous or surgical drainage [5,10,11]. EUS-guided drainage has a technical success rate of more than 90% and a clinical success rate of 75% to 90%, depending on the type of stent used [12-14].

LAMS is a new dedicated fully-covered SEMS for drainage of PFCs and overcomes the demerits of PS and FCSEMS. In addition to the wide biflanged shape of LAMS, a wide-diameter lumen provides a conduit for direct endoscopic necrosectomy as well as improved drainage, which obviates the need for repeated endoscopies. In our study, LAMS was placed in 2 patients with WON and both underwent clinically successful endoscopic necrosectomy. Currently, various types of LAMS have been introduced including a wide flared-end NAGI^TM stent (Taewoong Medical), BCF stent (MITech Co., Ltd., Seoul, Korea), and anchoring stent (AXIOS; Xlumena Inc., Mountain View, CA, USA). Several studies have shown that LAMSs have a very high rate of technical (89%–100%) and clinical (93%–100%) success [1,15-19]. LAMS provides stent stability, minimizes the risk of migration due to an anchoring effect, and enables a larger lumen for passage for easy direct access into the cavity for necrosectomy. Our study used SPAXUS^TM as LAMS (Fig. 1), which has wide anchoring flanges that can be folded back after placement to prevent migration and maintain tight apposition.

Although metal stents have been used to compensate for the demerits of PSs, few studies have compared the clinical outcomes between the 2 stents; results indicating the better stent are still controversial. There is no definitive evidence so far in published literature that favors the LAMS when compared with the PS in resolving PFCs. The choice of stent is based on the discretion of the endoscopist rather than evidence-based findings. In a recent comparative study between PS and LAMS, which enrolled 103 patients with PFCs including 84 who were drained using PSs and 19 using LAMSs, clinical success was similar between the 2 groups (96% vs. 94%, p=0.78) [1]. EUS-guided drainage for PFCs had a high technical success rate with either PS or LAMS in our study. This result consistently matches reports from other studies [4,15,20,21]. Previous published studies have reported that the technical success rate of PP drainage using PSs ranges from 84% to 98%, whereas the rate of success when LAMSs are used is 78% to 100% [1,2]. Although many previous studies, including our study, showed no difference in clinical outcomes, different types of metal stents used and different times of evaluation may affect the rate of clinical success. Therefore, further controlled prospective comparative studies are required to validate the superiority of LAMS over PS.

While some reports have shown that more AEs occurred in PS placements (odds ratio, 2.9; 95% confidence interval, 1.4–6.3) compared to that in metal stent placements [2,22], other studies have shown no difference in AEs between the 2 stents (16% vs. 23%) in a systematic review [20]. Although our study showed no differences in the rates of technical and clinical success between the 2 stents, the procedure time was much shorter when using LAMS compared with PS (10.6±2.5 min vs. 21.4±9.5 min, p=0.002). The shorter procedure time in the LAMS group might be attributed to the simpler process requiring 1 stent and 1 guidewire, and little chance of AEs as well as additional benefits such as decreased patient discomfort and less radiation exposure may be expected [23]. However, the rate of procedure-related AEs was similar between the 2 groups in our study.

In previous comparative studies, bleeding in the metal stent was a major concern as procedure-related AEs. It is speculated that the reason for a high rate of bleeding in LAMS is perhaps the rapid decompression of the cystic cavity afforded by the large caliber of the LAMS, causing friction or irritation of the vasculature within the cavity [24]. Other studies have proposed that the wide lumen of the LAMS may allow for more entry of gastric acid into the cyst cavity, in which low pH fluid may irritate the exposed intracavitary vessels and promote bleeding [1]. However, no episode of bleeding occurred in the LAMS group in our study. Thus, further prospective studies may be required to elucidate which subsets of patients and patient characteristics may have increased risk of bleeding.

Although the result of our study did not reveal the superiority of LAMS in clinical outcomes and recurrence of PFC management, the reduced procedure time is a strength of our study, which was attributed from easy procedure technique.

There are some limitations of our study. First, the retrospective review of a small number of patients and heterogeneity of baseline patient characteristics between the 2 groups are the main limitations. Only 2 cases with WON were included in the LAMS group. Therefore, we were not able to equally select the stent for the procedure and had no choice to adjust the duration of follow-up or stent duration, which may have affected the results. Second, before the introduction of LAMS in October 2016, all procedures were performed with double-pigtail PSs; thereafter, LAMS was used for all patients with PFCs. Thus, there is a possibility that external factors such as the development of devices may have acted as a bias. Furthermore, the duration of follow-up was different between 2 groups and exerted bias in baseline characteristics. Third, the number of patients with clinical success and patients included in the recurrence analysis were somewhat different. Four patients in the PS group did not follow up after stent insertion in 1 or after stent removal in 3. Therefore, we could not judge the recurrence. Finally, the mean duration from the time of stent insertion to the time of the first follow-up CT between the PS and LAMS groups (66.8 days vs. 29.4 days, p=0.032) was significantly different. These differences may have acted as a bias in evaluating recurrence.

In conclusion, our study showed that PS and LAMS have similar clinical outcomes for drainage of PFCs. However, LAMS was associated with a shorter procedure time. At present, it is suggested that LAMS is an ideal stent and is highly recommended for treating PFCs in terms of antimigration and direct access to WON. Further prospective randomized studies including a larger number of cases are needed to validate the optimal management strategy for patients with PFCs.