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(Chest. 2005;127:482-487.)
© 2005 American College of Chest Physicians

Removal of Covered Self-Expandable Metallic Airway Stents in Benign Disorders*

Indications, Technique, and Outcomes

Marc Noppen, MD, PhD, FCCP; Grigoris Stratakos, MD; Jan D’Haese, MD; Marc Meysman, MD, FCCP and Walter Vinken, MD, PhD

* From Interventional Endoscopy Clinic, Respiratory Division, University Hospital AZ-VUB, Free University of Brussels, Brussels, Belgium.

Correspondence to: M. Noppen MD, PhD, Head, Interventional Endoscopy Clinic, Respiratory Division, University Hospital AZ-VUB, Laarbeeklaan 101, B 1090 Brussels, Belgium; e-mail: marc.noppen{at}az.vub.ac.be


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Study objectives: To describe the technique and outcome of removal of self-expandable metallic airway stents (SEMAS) in a series of patients who underwent stenting for benign airway stenoses.

Design and setting: A retrospective cohort analysis of patients with benign airway disorders treated with SEMAS between 1997 and 2003, who presented with an indication for stent removal in a tertiary-care hospital, and referral interventional pulmonology clinic.

Patients and methods: During the study period, 49 SEMAS were inserted in 39 patients for treatment of benign airway disorders. Ten of these 39 patients (25.6%), bearing 12 covered stents, presented with an indication for stent removal. Data of these cases were extracted from electronic files kept in our institution archive.

Results: Indications for stent removal included excessive or recurrent granuloma formation (five cases), recurrence of stenosis after stent failure (one case), stent fracture (two cases), and accomplishment of treatment (two cases). In all of these cases, covered versions of SEMAS had been placed either in the trachea or in a main bronchus. In contrast to many previous reports, these stents proved to be absolutely retrievable even if some difficulties were encountered. In all cases, however, removal was successful without major complications. All patients resumed normal spontaneous ventilation postoperatively, and follow-up was uneventful. Average duration of stenting before removal was 16.2 ± 17.5 months (± SD) [range, 1 to 60 months].

Conclusions: We conclude that although placement of SEMAS is assumed to be permanent in patients with benign airway disorders, an indication for stent removal is often observed (25.6% in our series). The covered SEMAS can be effectively and safely removed if needed without major sequelae. Nevertheless, new technical improvements in metallic stent design and materials may help reinforce the concept of a retrievable metallic airway stent, which may offer significant clinical advantages.

Key Words: benign tracheobronchial strictures • central airways obstruction • interventional pulmonology • rigid bronchoscopy • self-expandable stents


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Surgical tracheal sleeve resection and reconstruction remains the "gold standard" treatment for most benign airway strictures.1 However, nonsurgical modalities such as laser photocoagulation and resection, balloon dilatation, and electrocautery have been developed to deal with airway stenosis not amenable to surgery. Endoscopic implantation of airway prostheses (stents) in these patients has gained increasing popularity over the last decade. Currently, various inoperable benign airway disorders are considered indications for airway stenting.12 Postintubation stenosis (PITS), tracheal burn or trauma, tracheobronchomalacia, and extrinsic compression of the trachea are the most common etiologies amenable to stenting. Due to their ease of removal and repositioning, silicone stents have extensively been used in the past when a benign disorder was encountered.345 Their disadvantages (high migration rate, small lumen-to-wall thickness ratio, and difficulty to clear secretions), however, prompted endoscopists to use self-expandable metallic airway stents (SEMAS) when silicone prostheses were unsuitable (ie, distal airway) or stent migration probability was judged too high (ie, tracheomalacia).678 Potential advantages of using metallic stents include smaller migration rate, greater cross-sectional airway diameter due to thinner wall construction, better conforming to irregular airways, and epithelialization within the stent allowing for maintenance of mucociliary clearance, not to mention a greater ease of placement, which in some cases may lead to inappropriate use.9 Disadvantages of this type of stent in benign disorders include difficult repositioning or removal after deployment due to their embedding in the bronchial mucosa and epithelialization of the inner surface. Granuloma formation at the extremities (or within the stent wall if uncovered) is a relatively common inconvenience of both type of stents (silicone or metal) possibly resulting from the radial force applied against the airway wall and the friction exerted. This complication often requires repetitive interventions to treat granulomas or replace the prosthesis, thus making patient management more difficult.1011 Existing published experience with second-generation SEMAS (Wallstent and Ultraflex; Boston Scientific; Galway, Ireland) is quite limited and almost uniformly describes them as "permanent" or as "difficult to remove."121314 In several cases however, stent removal or replacement is imposed by the presence of various complications, disease relapse, or treatment failure or even treatment accomplishment. Pediatric patients represent another common indication for stent removal or replacement.15

In this study, we evaluated retrospectively metallic stent removal in patients with benign disorders treated in our institution during the last 7 years. We report on the indications, technique, outcomes, and complications of these stent removals.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
We retrospectively analyzed data on all patients with benign disorders who received SEMAS between 1997 and 2003. Data were extracted from electronic files of our institution archive.

Forty-nine SEMAS (41 covered Ultraflex stents, 6 uncovered Ultraflex stents, and 2 Wallstents) were inserted by rigid bronchoscopy in the central airways of 39 patients hospitalized for benign airway disorders in our institution. There were 24 male and 15 female patients (mean age, 59 ± 16 years [± SD]; range, 16 to 95 years).

All patients were admitted for severe dyspnea caused by central airway obstruction as confirmed by fiberbronchoscopy. Indications are listed in Table 1 . All patients were nonsurgical candidates due to contraindications to surgery (ie, critically ill or with severe comorbidities or presenting very long, malacic, and complex stenoses), or because patients declined surgery after extensive multidisciplinary counseling.


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  		Table 1. Benign Indications for Placement of SEMAS

 
In most cases, SEMAS were preferred because of the presence of a malacic portion of the trachea and/or major bronchi, or when an irregular and small airway was involved making the use of Dumon silicon stents unsuitable. Since published experience of metallic autoexpandable stent removal was quite limited and these stents generally have been described as "nonretrievable," their deployment was initially considered permanent. After stent placement, patients had to quit smoking and were prescribed normal saline solution nebulizations twice daily.

Technique Description
When indicated and after informed consent by the patient, removal of stents was performed with rigid bronchoscopy (Karl Storz; Tutlingen, Germany) in a fully equipped operating theater under total IV anesthesia (IV propofol, alfentanil, and atracurium). Ventilation and oxygenation were ensured by high-frequency jet ventilation with variable fractional inspiratory oxygen concentrations delivered by a side port of the bronchoscope.

Removal was performed by grasping the circular extraction loop or if impossible, one of the metallic loops of the proximal edge of the stent with a rigid alligator forceps. Meanwhile, the beveled edge of the rigid scope was advanced coaxially until the proximal edge of the stent was introduced in the inner lumen of the scope, thus creating a space between the stent wall and the airway mucosa. Immediately after that, pulling the stent extremity with the forceps together with a turning movement of the rigid bronchoscope allowed for successful removal of the stent, which in many cases was retrieved intact (Fig 1 ). Although successful at the end, this procedure proved demanding in both bronchoscopic skills and operating time. If the stent broke during this process, the remaining threads would be removed piecemeal with the forceps through the rigid bronchoscope.



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  		Figure 1. Two covered Ultraflex stents endoscopically removed 2 years after placement (patient 10). Granuloma formation can be seen on the proximal edge of one of the stents (arrows).

 

   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
Ten of the 39 patients (25.6%), all of them bearing covered versions of SEMAS, presented with an indication for stent removal during the follow-up period (5 male and 5 female patients; mean age, 48 ± 15 years; range, 16 to 62 years). Indications for removal included restenosis due to excessive or recurrent granuloma formation impossible to manage with other treatment modalities (five cases), relapse of stenosis after initial treatment due to material fatigue (one case), stent fracture (two cases), and accomplishment of treatment (two cases) [Table 2 ].


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  		Table 2. Clinical Characteristics of Patients Who Presented With an Indication for Stent Removal*

 
Presenting symptoms were recurrence of dyspnea in six cases, foul breath and purulent expectoration in two cases, while the remaining two patients were asymptomatic and indication for removal of prosthesis was documented by follow-up fiberbronchoscopy. Average duration of stenting before indication for removal was 16.2 ± 17.5 months (range, 1 to 60 months). We were able to remove all 12 stents in the 10 patients (11 from the trachea and 1 from the left main bronchus, all covered Ultraflex stents).

Significant oozing and tracheal mucosa dehiscence occurred in only two patients and could be controlled by bronchoscopic techniques (tamponade by means of the shaft of the bronchoscope). Small pieces of metallic wire totally embedded in the tracheal or bronchial mucosa remained in place in three cases, as it was impossible to remove them without causing major trauma to the airway mucosa. These small metallic threads have been followed up bronchoscopically (Fig 2 ). They have remained stable and have not caused any complications. However, a longer follow-up period is required to exclude long-term sequelae. No other complications were observed. All patients resumed normal spontaneous ventilation postoperatively, and no late complications related to the procedure occurred.



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  		Figure 2. Bronchoscopic view of the trachea 2 months after removal of the self-expandable metallic stents. Healing of the mucosa is evident, although the imprints of the mesh are still recognizable. A small peace of embedded metallic thread is still visible (arrow), but has not caused complications during follow-up.

 
All five patients with stent-related granuloma formation had undergone multiple interventional bronchoscopic treatment trials including cryotherapy, mechanical excision, or balloon dilatation prior to the decision for stent removal (Table 2). In two of these patients, tracheostomy had to be performed after removal of airway prostheses, due to their critical health status considered not amenable to other interventional or conservative treatment. One patient with tracheomalacia who presented a marked tendency for granulomas and keloids received brachytherapy treatment,1617 with excellent results. In the remaining two patients of this subgroup, new stents had to be deployed due to continuing need for airway wall support. Stent replacement was also necessary in the two cases of stent rupture as well as in the case of stent failure due to material fatigue 2 years after first placement. In two patients in whom treatment was judged accomplished, the presence of stents was no longer indicated; they were dismissed after stent removal without any other treatment and follow-up was uneventful.


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
The management of patients with tracheobronchial strictures of benign etiology can be quite challenging. There are a large number of patients with lesions not amenable to surgery, or who are considered medically inoperable.2 In these patients, airway stenting may represent the only possible treatment. Silicone prostheses are considered the first choice in benign diseases except in cases where they are judged unsuitable because of airway wall malacia or distal and/or angular stenosis. In such cases, SEMAS are generally indicated.1678 Although SEMAS have systematically been used during the last decade to manage benign tracheobronchial strictures with well-documented positive results, their use for this indication is still debated.1114

Despite their more advantageous internal/external diameter and decreased risk of migration, the major drawback for placement of the currently used SEMAS in benign situations is their difficult repositioning and removal in case of complications. Reports on these removals are scarce in the literature,13141518 and the overall impression is that placement should be considered permanent and therefore restricted to patients with a short life expectancy.218

In our series of 39 patients treated with SEMAS of second generation (Wallstent and Ultraflex), 10 patients (25.6%) presented with an indication for removal. In all of the cases, it was the polyurethane-covered expandable Ultraflex stent that had to be removed. It is possible that if patients with the uncovered version of the same stent had presented with an indication for stent removal, results would have been different.

Five of the 10 patients had excessive and recurrent granuloma formation for which other means of treatment were exhausted. Granuloma formation is a common complication of airway stents. The constant friction of stents and the highly localized pressures they exert against the mucosa possibly promotes the development of granulation tissue. Ideally, a stent should fit tightly and should not move to avoid friction. An undersized stent would exert excessive friction of the metal against the airway wall, while an oversized one would exert excessive radial pressure alongside the bronchial mucosa and impair microcirculation.119 It is therefore of cardinal importance to select the proper size of stent and make sure its edges are smooth.

In our series of SEMAS placed for benign tracheobronchial strictures (39 patients) during a follow-up period of up to 6 years, we observed granuloma formation over the edges of the stent or through its metallic meshes in 17 patients (43%) requiring several interventional bronchoscopy procedures including cryotherapy, balloon dilatation, or mechanical excision. Only 5 of those patients (or 12.8% in our series), however, had to have their stents removed. As life expectancy of patients with stents is getting longer and more benign indications are recognized for airway stent insertion, the high rate of granuloma formation over the stent will become more of concern and a major limitation.

The mesh of the Ultraflex stent is made of Nitinol, a highly bioadaptable nickel-titanium alloy exhibiting low resistance to cough yet adequate resistance to airway compression. Stent fracture or failure due to metal fatigue after some years of continuous strain may develop in a number of patients and call for stent removal (three cases or 7.7% in our series). Metal fatigue of the mesh and spontaneous expulsion of wire stent fragments (metalloptysis) have been previously reported.1920 No specific contributing factors (trauma, emergency intubation, recurrent infections, or persistent cough) could be identified in our patients; the short duration of treatment (5 months and 6 months, respectively) also is unlikely to contribute to the rupture or fatigue of the stent.

Strengthening of the airway wall can be observed after some years of stenting, making further mechanical support unnecessary. For silicone stents, several studies421 have reported 18 months as a proper duration of stenting before removal is attempted, but no data on SEMAS are available. In our series, we postulated treatment accomplishment in two cases (5.1%), one with a PITS, and another with a malacic stricture resulting from external compression of trachea by a large goiter. Durations of stent treatment were 5 years and 1.5 years, respectively. Stability of the bronchoscopic appearance and the informed patient request were the major criteria for attempting removal in these two patients. No recurrence or other complication followed stent removal, and both patients could be dismissed from hospital without further treatment.

We were able to remove all 12 covered Ultraflex stents from our patients. To our knowledge, there is no other published report of a similar series of stent removal. No major complications occurred during the removal procedure. In two cases, oozing occurred, which could be easily controlled after tamponade with the shaft of the bronchoscope. This is in accordance with previous scarce case reports1012131419 of stent removal, where only minor bleeding was observed. Dehiscence or laceration of the tracheal mucosa was amazingly self-healing, and in both patients in whom we observed this phenomenon, no sign of scar or trauma was seen 2 months after intervention (Fig 2).


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
Although placement of SEMAS is assumed to be permanent in patients with benign airway disorders, an indication for stent removal is often observed (25.6% in our series). The results obtained in our study suggest that covered SEMAS can be both effectively and safely removed if needed without major sequelae. However, removal can be cumbersome in inexperienced hands. Efforts are ongoing to produce better-designed, technically improved, removable airway stents that may be more suitable for pediatric use and for patients with long life expectancy.2223 Newer improvements in organic materials (poly-L-lactide) have also led to experimental studies in animals, testing bioabsorbable airway stents, which would not have to be retrieved at all.2425 These new technical improvements in self-expandable stent design and materials may offer considerable clinical benefits in the future.


   Footnotes
 
Abbreviations: PITS = postintubation stenosis; SEMAS = self-expandable metallic airway stents

Received for publication January 20, 2004. Accepted for publication August 27, 2004.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

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