## 4 Discussion  
The primary aim of our present study was to test the feasibility of stent insertion into the ET from the nasopharynx under endoscopic guidance in a porcine model. We inserted commercially available metallic stents with endoscopic guidance and subsequently validated their successful placement using fluoroscopy, CT scans, and necropsy. The introduction of BET interventions allowed the surgical management of an obstructive ETD. Since 2010, studies have reported the use of BET in ETD, with success rates of 36%-80% [8; 10; 12; 13; 17]. Although these prior studies all reported that BET was superior to conventional medical management, this dilation treatment was not successful in some cases, necessitating a further management option. Stents are commonly used for the treatment of obstructive disorders in many non-vascular systems, such as the digestive, respiratory, and urinary tracts [18; 19; 20]. However, there have been no attempts to use stents for the treatment of obstructive ETD and side effects have been reported for stent insertions into the non-vascular luminal organs. The development of new strictures due to stent-induced tissue hyperplasia caused by mechanical injuries remains a significant obstacle to successful stent placement in non-vascular luminal organs [18; 19; 20; 21]. Another cause of stent re-obstruction is biofilm formation with infections on the stent surfaces [22; 23; 24]. Our histological results also demonstrated severe tissue hyperplasia through the stent strut in the porcine ET at 4 weeks after stent placement. Various functional stents, such as drug-eluting biodegradable or non-biodegradable and nano-functionalized stents using gold or silver nanoparticles, have been investigated using various stented animal models to overcome these problems [25; 26; 27; 28]; however, therapeutic strategies for the treatment of obstructive ETD that could be tested in human clinical trials have yet to be developed. Various stented animal models have been introduced to study the mechanisms of stent-induced stricture formation [25; 26; 27; 28; 29; 30]. Herein, we introduced a well-established ET porcine model to study the mechanisms of complications of stent insertion for ETD and developed a system to reliably test stent materials and configurations. We utilized cobalt-chrome alloy stents in our current analysis to test the technical feasibility of inserting a stent into the ET. The stent materials that have been used for the treatment of obstructive disorders in other systems include stainless steel, cobalt-chrome  
Figure 5: Representative histologic (hematoxylin and eosin staining at 1.25\(\times\) (**a**), 20\(\times\) (**b**), and 10\(\times\) (**c**)) and endoscopic images at 4 weeks after stent placement. (**a**) Microscopic image of a histologic section. (**b**) Severe inflammatory cell infiltration (arrowheads) adjacent to the stent strut (arrows). (**c**) Tissue hyperplasia with increased submucosal fibrosis through the stent strut (arrows). (**d**) Follow-up endoscopic image obtained 4 weeks after stent placement showing the stent (arrows) in place and the proximal end of the stent filled with secretion (arrowheads). alloy, nitinol wire, and biodegradable substances [31; 32; 33]. The ideal stent material should be biocompatible and radiopaque, relieve symptoms caused by obstructive disorders, have low foreign body sensation, not induce susceptibility to infection, and be available at a reasonable cost. The cobalt-chrome tested in the present study was readily available because it is commonly used in coronary arterial disease [34]. However, this material has some disadvantages, including a lack of MRI compatibility, poor fluoroscopic visibility, and non-elastic force [35]. Stents made from nitinol, a shape memory alloy with super-elastic properties, are commonly used to treat obstructive disorders in non-vascular systems, such as those of the digestive, respiratory, and urinary systems [18; 19; 20].