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Ann Thorac Surg 2008;85:S792-S796. doi:10.1016/j.athoracsur.2007.11.051
© 2008 The Society of Thoracic Surgeons
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Supplement: The Minimally Invasive Thoracic Surgery Summit

Airway Stents

Cynthia S. Chin, MD*, Virginia Litle, MD, Jaime Yun, MD, Todd Weiser, MD, Scott J. Swanson, MD

Department of Cardiothoracic Surgery, Mount Sinai Medical Center, New York, New York

* Address correspondence to Dr Chin, 1190 Fifth Ave, Box 1028 GP2W, New York, NY 10029 (Email: cynthia.chin{at}mountsinai.org).

Presented at the Minimally Invasive Thoracic Surgery Summit, New York, NY, June 8–9, 2007.


   Abstract
Top
 Abstract
Introduction
 Indications for Stent Placement
 Types of Stents
 Benign Disease and Stent...
 References
 
Airway stenting has been well used in the treatment and palliation of patients with malignant stenoses and to a lesser extent in those with benign disease causing airway compromise. Stents are either constructed of silicone or metal, usually a nitinol, a nickel and titanium alloy. The different categories of stents have positive and negative attributes that play a role in choosing the proper stent. This article aims to discuss these issues with regards to malignant and benign tracheobronchial disease.


   Introduction
Top
 Abstract
 Introduction
Indications for Stent Placement
 Types of Stents
 Benign Disease and Stent...
 References
 
The National Cancer Institute projects there will be 213,380 new cases of lung cancer this year [1]. Surgery is the treatment of choice for those patients with early-stage lung cancers; unfortunately, most patients will have advanced lung cancer at the time of diagnosis. These patients branded with a poor prognosis may not benefit from surgery with a curative intent; however, they will require procedures for palliation with the hopes of providing a reasonable quality of life. It has been reported that in up to 30% of patients with lung cancer, central airway obstruction will develop that may be secondary to endoluminal disease or external compression by a hilar tumor or bulky lymphadenopathy [2–5]. In these patients it becomes imperative that palliative therapy be considered for symptomatic relief and improvement of quality of life.

Strictures and critical stenoses may result from benign causes such as postintubation or posttracheostomy endothelial trauma, Wegner granulomatosis, or tuberculosis. For benign disease amenable to surgery, resection and reconstruction is the gold standard of therapy; however, for those patients who are not surgical candidates because of disease or existing comorbidities, endoscopic therapies are needed.


   Indications for Stent Placement
Top
 Abstract
 Introduction
 Indications for Stent Placement
Types of Stents
 Benign Disease and Stent...
 References
 
Malignant central airway compression produces dyspnea, stridor, hemorrhage, or obstructive pneumonia, or a combination. Indications for use of stents in this disease include but are not limited to the list in Table 1. The only definitive contraindication for placement of an airway stent is when there is external compression of the airway by a vessel. Patients in whom these stents were placed had an unacceptably high rate of erosion, hemorrhage, and death [6]. Although other palliative options will not be discussed in detail, the use of several interventions in conjunction with stents cannot be over emphasized [6–10].


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  		Table 1 Indications for Central Airway Stents
 
Brutsche and colleagues [11] recently reported the outcomes of treated advanced non-small cell lung cancer with and without airway obstruction. They studied 144 patients with advanced disease who were receiving palliative chemotherapy to see if central airway obstruction was a negative prognostic factor. The patients with obstruction had treatments with laser alone (25%), stent alone (25%), or both (50%). Median survival was 8.4 months (range, 4.8 to 17.1 months) in the patients without airway obstruction and 8.2 months (range, 3.7 to 17.9 months) in those with central airway obstruction, which was not a significant difference (p = 0.395). Airway compression does not appear to be a poor prognostic sign in these patients, but they may benefit from stenting of the obstruction to improve their quality of life.

Benign strictures secondary to inflammatory and infectious disease may need to be stented if the patient’s disease process or comorbidities prohibit definitive surgical repair. Another group of patients who may benefit from placement of endobronchial stents are lung transplant recipients. Airway dehiscence develops in a small percentage of these patients in the immediate perioperative period, or stricture develops weeks to months after transplantation. These complications have been attributed to bronchial blood supply of the donor lung, perioperative infection, and immunosuppression. Airway complications drastically improved in the early years of lung transplantation; however, the incidence of such complication in the last decade has not changed greatly and endobronchial therapies are still required [12].

An endobronchial prosthesis needs to fulfill many requirements to be considered ideal. An airway stent for palliation should, most importantly, reestablish the airway with minimal morbidity and mortality. Table 2 lists the characteristics of an ideal stent; however, such a stent is not in existence.


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  		Table 2 Characteristics of an Ideal Pulmonary Stent
 

   Types of Stents
Top
 Abstract
 Introduction
 Indications for Stent Placement
 Types of Stents
Benign Disease and Stent...
 References
 
Many types of stents are available from many different manufacturers. In general, they can be classified into one of four categories (Table 3). Most modern day silicone stents are derived from the Montgomery T tube, which was originally described in the 1960s [13]. The Montgomery T tube has a side arm that requires a tracheostomy. The silicone stents inhibited mucociliary mechanisms that clear the airway of secretions. Dumon developed a silicone stent with studs on the outer wall to decrease impairment of cilia. This stent was also the first stent that did not necessitate the formation of a tracheal stoma [14]. Silicone stents have the advantage of being easily removed and exchanged when needed, and they are relatively inexpensive. This is important in patients who respond to systemic treatment of their disease because their airway can be reevaluated after removal of the silicone stent.


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  		Table 3 Types of Stents
 
One of the largest studies of silicone stents was published by Dumon and colleagues [15]. In three European centers, 698 patients had silicone stents placed for malignant airway obstruction. Stent migration was reported as the most common complication (9.5%), followed by granulation tissue formation (8%) and mucous plugging (4%).

Wood and colleagues [16] reviewed their single institutional experience with endobronchial stents from 1992 to 2001. Stents were placed in 143 patients for malignant and benign stenoses. Silicone stents with proximal and distal flanges and exterior studs were used in 87% of the patients, and metal stents were used in the other 13%. In addition to stent placement, some patients required other interventions, including rigid bronchoscopy coring-out in 18%, balloon dilation in 11%, brachytherapy in 3%, laser in 3%, and photodynamic therapy in 1%. Stents were placed in 5 patients for compression from mediastinal lymphoma or germ cell tumor. Four of the 5 stents were removed after completion of therapy. The level of difficulty in retrieving the stent was not mentioned. A bronchoscopic procedure was done in 59% of patients, but 21% required two procedures, and 6% required three procedures. Complications occurred in 42% of the procedures, with the most common being retained secretions (27%), followed by granulation tissue formation (9%) and stent migration (5%). No patients died; however, airway perforation was seen in 4 patients, and 1 required an operation. Overall, 95% of the patients reported significant improvement in symptoms.

In contrast to the silicone stents, endobronchial metal stents were less likely to inhibit the respiratory cilia or dislodge. The early generation of endobronchial metal prostheses were developed from endovascular stent technology. The metal is usually steel or nitinol. These stents (Strecker, Palmaz) required a balloon to be placed into the stent, after it was in proper position, so it would expand to meet the walls of the lumen. This cumbersome step was eliminated with the advent of the self-expanding metal stents (SEMS).

The SEMS have become popular endobronchial prostheses owing to the relative ease in placement. These stents are compressed into a small delivery device, and once deployed, a radial force embeds the stent into the surrounding tissue. They can be positioned and deployed with a flexible bronchoscope, which allows some patients to have this placed in an outpatient setting. These stents have the potential for tumor in-growth along the length of the stent. As a result, the uncovered metal stents are used to the most benefit in patients with extraluminal airway compression [17]. The biggest disadvantage of these stents is they are permanent. Once seated and incorporated, they can be difficult if not impossible to remove.

The covered SEMS (Ultraflex and Wallstent, both Boston Scientific/Microvasive, Natick, MA) were developed as a hybrid of silicone and metal stents. They have a decreased risk of tumor in-growth and granulation tissue formation except at the ends, which are kept bare for anchoring to the mucosa. This last feature gives them the shared advantage with their uncovered counterparts of decreased migration compared with silicone stents. They are more easily removable than the uncovered stents; however, granulation tissue in-growth at the ends makes them harder to remove than the pure silicone stents. Several disadvantages of metal stents include their high cost, difficulty moving them once deployed, and the in-growth of granulation tissue that leads to reocclusion of the lumen.

A large, single-institution retrospective review was done by D’Amico and colleagues [18]. Of the 172 patients with stent placement between 1997 and 2003, 140 had malignant disease. Contrary to Wood and colleagues, their institutional preference was metal stents. Self-expanding metal stents were placed 166 of 172 patients, and the rigid metal stents were placed in the other 6 patients. Silicone prostheses were not used. No intraoperative deaths were associated with stent placement. Complications occurred in 23 patients, of which the most was tumor in-growth in 9, followed by granulation tissue formation in 7, migration in 5, and external compression leading to restenosis in 2. Stent removal was performed in 5 patients, but the details were not described.

A new advancement in silicone stents was the development of the Polyflex stent (Boston Scientific), which had a thinner wall and could conform better to the airways than its traditional counterparts. The Polyflex stent had problems with migration [19], which was reportedly decreased with the addition of studs on the outer surface [20].


   Benign Disease and Stent Placement
Top
 Abstract
 Introduction
 Indications for Stent Placement
 Types of Stents
 Benign Disease and Stent...
References
 
In addition to inflammatory disease and long tracheobronchial strictures nonamenable to surgery, stents have been placed in postlung transplantation strictures with a reported 83% immediate improvement of dyspnea after placement [21]. Mughal and associates [22] reported their experience in 7 patients with high-grade anastomotic dehiscence after lung transplantation. They believed the mortality rate from a second operation would be too high, so they choose uncovered SEMs, which allowed drainage of the mediastinum. Two patients died, one from a pulmonary embolism and the other from multiorgan failure. In the other 5 patients, they believe the ingrowth of granulation tissue helped heal the dehiscence. They found the stents could be removed without difficulty 6 to 8 weeks after placement.

The occurrence of obstructing granulation tissue after stenting is reported to be 12% to 28% in patients with benign disease [23–26]. In-stent granulation tissue has been treated successfully with one or more sessions of laser resection or electrocautery [24, 27]. The formation of in-stent granulation tissue requiring multiple treatments has led to the development of retrievable stents that would be removed after treatment was complete.

In performing a systematic review of the literature, we found 7 published reports by Song and colleagues [28–34], who have been investigating a stent and retrieval hook they designed. Their findings across these publications suggest that their nitinol stent is easily removed with minimal to no complications. They have reported its use in benign and malignant disease as well as in tracheoesophageal fistulas. These case series are small and performed in a retrospective manner.

Li and colleagues [35] described the successful use of a Hans stent in the treatment of bronchopleural fistula. The stents were removed in 7 of the 8 patients after successful closure of the bronchopleural fistula without any complications noted. Finally, Noppen and colleagues [36] reported the removal of 10 covered stents. Bleeding and mucosal dehiscence occurred in 20% of the patients, and parts of the wire from the stents were left in 33.3% of the patients.

Publications on retrievable metallic stents are scarce. It has been well documented that the silicone stents are easily removed and exchanged. Many publications report on covered metal stents and their complications, but no large series has described the level of difficulty and complications associated with removal of the covered stents. And to date, no large randomized trial has compared silicone stents and metal stents.

In conclusion, patients with life-threatening airway obstruction secondary to a malignant cause can benefit from endobronchial interventions, which can help return these patients to a significant quality of life [9–11, 37]. Relief of central airway obstruction with an endobronchial prosthesis may result in resolution of a postobstructive pneumonia, which may allow a small percentage of patient to receive chemotherapy not given in the presence of an infection or to undergo a surgical procedure. Relief of a stenosis may provide symptomatic relief that can bridge the patient until further therapy is initiated.

Many advantages as well as disadvantages are associated with each type of endobronchial stent. There is no ideal stent, and no data have shown an absolute benefit of one stent rather than another [38–42]. In patients with benign disease and a reasonable life expectancy, permanent stents are not ideal because of in-stent granulation tissue formation. Retrievable stents are being investigated to help alleviate this problem, but they do not fulfill the requirements of an ideal stent. We need to continue to investigate this technology to allow us to palliate and treat patients whose disease or poor medical condition precludes surgical therapy.


   References
Top
 Abstract
 Introduction
 Indications for Stent Placement
 Types of Stents
 Benign Disease and Stent...
 References
 

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