Airway stents

INTRODUCTION — Airway stents, also known as tracheobronchial prostheses, are tube-shaped devices with a hollow lumen that are inserted into an airway. They are usually placed bronchoscopically and can be used to treat a variety of large airway diseases.

The indications for airway stenting, types of stents, insertion technique, complications, and their removal are reviewed here. Strategies for managing central airway obstruction are discussed separately. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults".)

PATIENT SELECTION

Indications — In general, airway stenting is a palliative therapy or bridge to curative therapy for patients with several types of airway diseases, among which central airway obstruction (CAO) due to malignancy is the most common [1-14] (table 1). The specific details of the indications for stent placement in patients with the following conditions are discussed separately:

●Nonmalignant or malignant CAO (see "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults")

●Benign or malignant tracheal- or bronchial-esophageal fistula (see "Tracheo- and broncho-esophageal fistulas in adults" and "Bronchopleural fistula in adults" and "Alveolopleural fistula and prolonged air leak in adults")

●Tracheo- and tracheobronchomalacia (see "Tracheomalacia in adults: Clinical features and diagnostic evaluation")

●Anastomotic dehiscence following lung or heart-lung transplantation (see "Airway complications after lung transplantation", section on 'Bronchial necrosis and dehiscence')

Contraindications — Airways stents are generally inserted bronchoscopically using either general anesthesia or moderate sedation. Thus, contraindications to bronchoscopy, general anesthesia, and/or moderate sedation are also considered contraindications to airway stenting. These are reviewed separately. (See "Flexible bronchoscopy in adults: Indications and contraindications" and "Overview of anesthesia" and "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications", section on 'General considerations and precautions'.)

Airway stenting is almost always performed after thermal ablation (eg, laser therapy, electrocautery, argon plasma coagulation, or cryotherapy) of obstructing tissues because of a risk of stent obstruction and stent fracture, if thermal ablation is deployed close to the stent [15]. In contrast, external beam radiation therapy and brachytherapy are not contraindications to airway stenting and among thermal ablation techniques, cryotherapy is sometimes performed in patients with stents. (See "Bronchoscopic laser in the management of airway disease in adults" and "Endobronchial electrocautery" and "Bronchoscopic argon plasma coagulation in the management of airway disease in adults".)

Efficacy — CAO due to malignancy is the most common reason for stent placement and most of the data to support the efficacy and adverse effects of airway stents are derived from this population. In most cases, the successful placement of an airway stent results in the immediate improvement of symptoms associated with the underlying disorder (eg, dyspnea, cough, and/or respiratory insufficiency) [1,2,16-24]. In addition, improvements in lung function [25-29], exercise capacity [30], and quality of life should also be expected [1,2,16-21]. However, complications are not infrequent, and since most stents are placed for palliative reasons in patients with lung cancer, airway stents do not prolong survival.

Data that support efficacy for each of the indications are discussed in the individual topics of interest.

●(See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults", section on 'Airway stent'.)

●(See "Tracheo- and broncho-esophageal fistulas in adults", section on 'Airway stent'.)

●(See "Bronchopleural fistula in adults", section on 'Stents'.)

●(See "Alveolopleural fistula and prolonged air leak in adults", section on 'Bronchoscopic interventions'.)

●(See "Tracheomalacia in adults: Treatment and prognosis", section on 'Stent trial'.)

●(See "Airway complications after lung transplantation", section on 'Management'.)

TYPES OF STENTS — Stents are made from several different materials and are available in varying sizes, shapes, and diameters (picture 1). The main classes of stents are silicone stents, metal stents (covered or uncovered), and hybrid stents (metal covered with either silicone or polypropylene or other covering). Newer-generation stents are brought to market frequently and so, this section describes the most common stents used, and is not a comprehensive list of all available stents. The advantages and disadvantages of each stent need to be appreciated prior to selecting a suitable stent for patients use (table 2). (See 'Choosing a stent' below.)

Silicone stents — Silicone stents have been available since the mid-1980s and are one of the most common types of stent used in clinical practice.

●Advantages – The following are considered advantages of silicone stents compared with uncovered metal stents:

•Silicone stents are firm and durable – Silicone stents resist extrinsic compression from tumor, enlarged lymph nodes, and circumferential fibrotic scars, and may be less prone to stress-fracture.

•Silicone stents have a lower frequency of granulation tissue and tumor infiltration. Although granulation tissue and tumor can develop at the proximal and distal ends of silicone stents, it occurs at a lower frequency than with uncovered metal stents. This feature together with their durability make silicone stents good for long-term (eg, >500 days) or indefinite use.

•Silicone stents are easier to reposition and remove using rigid grasping forceps – This feature is ideal when repositioning or removal is indicated for adverse effects and when serial stents of increasing size need to be placed for patients with stenosis too narrow for airway dilation prior to stent placement.

•Silicone stents are significantly less expensive than metallic or hybrid stents.

●Disadvantages – The following are considered disadvantages compared with uncovered metal stents:

•Silicone stents have a higher rate of migration (spontaneously or due to coughing) and infection when compared with metallic stents [24].

•Mucociliary clearance may be more inhibited with silicone stents, particularly longer stents, thereby increasing the risk of mucus plugs, impaction, and infection.

•Deployment (and removal) of a silicone stent usually requires rigid bronchoscopy and general anesthesia, although insertion via flexible bronchoscopy has been described anecdotally [31,32].

There are several types of silicone airway stents, some of which need specially designed loading devices:

●Studded stents – Studded stents have become the most widely used airway stents in the world (picture 2) [33]. They are manufactured in several different shapes, including straight, L-shaped, Y-shaped, and dumb-bell-shaped (mid-section that is slightly smaller in diameter than the proximal and distal ends) [34,35]. Y-shaped stents are primarily used for disease at the main carina, though can also be used to stent lesions that involve the secondary carina. These stent have small studs on the external surface to help prevent migration. These studs embed themselves slightly within the airway wall mucosa, but do not cause permanent damage; however, migration can still occur despite this feature. Large and small diameter stents can be custom-made.

●Smooth-walled stents – Smooth-walled stents are made by several manufacturers and were the first stents used prior to the creation of studded silicone stents [36]. They can be ordered in varying lengths and diameters, and shapes (picture 3). Newer versions have a small flange on the proximal and distal aspects to prevent stent migration. Despite this modification, stent migration still occurs.

●Reynders-Noppen tygon stent – A stent made from a cylindrical tygon plastic tube that has been molded into a screw-thread shape (picture 4) is available from one manufacturer [37]. A potential advantage is its rigidity and ability to resist significant extrinsic compression. It must be pushed into position along the outside of a specific introducer. This stent is available in Europe and Asia, but not in the United States.

Limited data are available that compare the efficacy of individual silicone stents. As an example, one study compared 50 patients with tracheal stenosis who were treated with two types of commercially available stents (smooth-walled and screw-thread) and, although migration may have been more frequently encountered with the smooth-walled stent (24 versus 5 percent), the difference was not significant [38].

Uncovered metal stents — Metal airway stents can be uncovered or covered (ie, hybrid). Uncovered metal airway stents are discussed in this section while covered metal stents are discussed below. (See 'Hybrid stents' below.)

Uncovered metal stents are self-expanding tubular meshes of crocheted filaments (also known as self-expanding metal stents [SEMS]). Except for dehiscence following lung transplantation, they are now uncommonly deployed, due to a Black Box warning issued by the US Food and Drug Administration regarding the increased risk of complications such as difficulty with removal due to epithelization/granulation tissue ingrowth, making them not suitable for long-term use, particularly in patients with nonmalignant lesions [39]. (See 'Stent-related' below.)

●Advantages – Uncovered metal airway stents have several advantages over silicone stents:

•Uncovered metal stents are usually inserted via flexible bronchoscopy, which requires only topical airway anesthesia and moderate sedation [40].

•Uncovered metal stents have excellent adherence properties to the airway wall and therefore rarely migrate.

•Metal stents have larger internal to external diameter ratio than silicone stents.

•The self-expanding characteristics may generate sufficient force to distend even the firmest of strictures, which is helpful if the airway cannot be dilated before stent insertion.

•Uncovered metal stents are radio-opaque and can be easily appreciated on chest radiography as well as chest computed tomography.

•Uncovered metal stents may be less likely to impair mucociliary clearance.

●Disadvantages – Compared with silicone stents, disadvantages of uncovered metal stents include:

•A greater risk of airway and vascular perforation due to their greater expansile force.

•Immense difficulty in removing or repositioning metal stents after epithelialization. This can sometimes lead to airway tears and stent fragmentation, further increasing the risk of associated complications. (See 'Removal' below.)

•Uncovered metal stents are associated with a greater frequency of granulation tissue or tumor growth through the spaces between the uncovered metal struts, and therefore have a greater potential to cause stent obstruction [41,42].

•Uncovered metal stents are less durable leading to more stent fracture (at 500 to 1000 days). This feature, therefore, makes them less desirable for long-term use (eg, >500 days).

•Metal stents are more expensive than silicone stents.

Several metal stents are available in varying lengths, shapes (including Y-shapes), and diameters (picture 5). Most are made of a single layer of braided or crochet metal (eg, stainless steel, nitinol [nickel-titanium alloy], cobalt alloy). In most cases before deployment, uncovered metal stents come in a compressed state. Special loading equipment or manipulation such as suture removal are required to allow the expansion of the stent to its target size, once it's in place. Some stents have flanges to prevent migration but most do not have this feature since migration is less of an issue, when compared with silicone stents.

Hybrid stents — There are several airway stents that incorporate two or more different materials. Such hybrid airway stents were designed to remedy the drawbacks of silicone stents and metal stents described above. As an example, a hybrid airway stent may consist of an expandable metal frame (resists compression) covered by a silicone membrane (limits the ingrowth of tumor or granulation tissue; ie, covered stents) [43-46]. Hybrid stents tend to be more expensive than airway stents that are made exclusively of one material. Some have small loops at the proximal and/or distal ends to aid with removal and repositioning. Some require rigid bronchoscopy for placement while others can be placed using a flexible bronchoscope.

There are several commercially available hybrid stents that come in different shapes, lengths, and sizes.

●There are several silicone-covered metal stents available. Some have a similar braided or crocheted design to the uncovered self-expanding metal stents but are partially or completely covered by a thin silicone membrane (picture 6) [44]; these hybrid stents maintain their expansile force but may be difficult to remove or reposition.

●Others have atraumatic extremities and are especially designed for placement in the bronchus and the carina (picture 7). Another hybrid stent consists of a silicone covered piece of nitinol may comply with irregular airway anatomy better than other stents ("shape-memory") but it is expensive and has a high migration rate (picture 8) [47].

●Y-shaped stents are also available such as has a firm anterior wall made of horseshoe-shaped metal struts and a posterior wall made of soft silicone (picture 9) [45]. The firm anterior and soft posterior walls simulate the trachea. This is a long hybrid stent, available in several lengths, that makes it an appropriate choice for patients with significant tracheobronchomalacia or long strictures involving the trachea and/or mainstem bronchi. This stent is difficult to insert (specially designed forceps deploy the stent during rigid laryngoscopy) and requires specific training. Another Y-shaped stent is a self-expanding hybrid stent where the absence of metal reinforcement at the level of the carina theoretically allows a more generous fit along the carinal ridge. Combinations of Y-shaped stents have been used in a custom design to palliate obstruction at both the main and peripheral carinas [35].

It should be noted that some "covered" stents leave the proximal and distal ends uncovered. This can be beneficial, when intentionally "jailing" a lobar bronchus since the uncovered part of the covered stent can allow for aeration and drainage of secretions, where the covered part of the stent prevents tumor ingrowth. As with all uncovered stents, however, epithelialization can occur making extraction quite difficult.

Investigational — Several investigational stents are in development.

Biodegradable stents — Biodegradable stents are constructed from a knitted polymer fiber (eg, polydioxanone) that degrades when placed inside the airway, making ultimate bronchoscopic extraction unnecessary (picture 10). They maintain their biomechanical strength for six weeks and dissolve completely after three to four months.

Biodegradable stents may be useful for airway conditions that need a temporary stent. Potential indications might include airway strictures secondary to lung transplant-related anastomotic complications [48], healing airway fistulas, or otherwise potentially curable benign strictures [49]. Case reports suggest possible use in pediatric patients with tracheobronchomalacia [50], although in some reports in infants, stent fragmentation reportedly caused life-threatening complications [49,51]. Other potential airway obstructions include toxicity from degradation products (eg, polyesters) and premature failure.

Drug-eluting stents — Drug-eluting stents are in development. These stents contain compounds (eg, paclitaxel) that prevent granulation tissue by inhibiting fibroblast growth [52,53]. Human trials are underway.

Bioengineered airway — The synthesis of new airways bioengineered from cryopreserved aortic allograft that generate newly synthesized trachea around custom-made stents has been successful in humans and is discussed separately. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults" and "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults", section on 'Investigational'.)

Three-dimensional (3D) printed airway stents — With the advent of 3D printing, some investigators are using computed tomography scans to tailor stent design to a particular airway, thus creating a "personalized airway stent." The US Food and Drug Administration released guidelines on 3D printing of medical devices [54]. Stent manufacture may include thermoelastic polymers, core silicone dipping, and silicone injection molding [55]. Four-dimensional (4D) printing is being investigated using complex smart polymers.

INSERTION TECHNIQUE — Airway stents should only be inserted and removed by clinicians trained in their use. Ideally, the provider should be able to place all types of stents and choose the best stent for the specific patient and not be limited to only placing stents that can be placed via flexible bronchoscopy.

Choosing a stent — Whenever a lesion amenable to stenting is identified, the distance, length, shape, and diameter of the lesion, as well as the proximity to proximal and distal patent airways should be evaluated. This should be done both bronchoscopically and by reviewing chest computed tomography (CT) in axial, coronal, and sagittal planes. Once this is complete, the optimal airway stent can be selected and insertion planned. It is advisable to have a large stock of stents available so that the most appropriate one for each individual patient may be chosen. Custom-made airway stents can be ordered from several manufacturers. In some patients, multiple stents may be placed.

Choosing a stent (type and size) depends upon the type, size, and location of lesion being treated, the future length of time that it will likely be needed, the patient’s preference, cost, and the expertise available. When choosing a stent, the advantages and disadvantages of each stent should be taken into consideration. The advantages and disadvantages of each stent are summarized in the table (table 2) and discussed in detail above. Typically only central airways (trachea, mainstem bronchi, bronchus intermedius) can be stented but there is a growing trend for stent insertion in smaller airways [56]. (See 'Types of stents' above.)

As examples:

●For patients with nonmalignant stenotic lesions, most experts choose a silicone stent. Dilation may be required prior to silicone stent placement and sequential stents of increasing size can be inserted over multiple procedures since silicone stents are easily removed and replaced. Uncovered metal stents should only be used in patients with nonmalignant stenosis after other options have been attempted, and by experts in complex airway management since a black box warning from the United States Food and Drug Administration has been issued to avoid their use in patients with non-malignant strictures due to an increased rate of complications with such devices [39]. (See 'Uncovered metal stents' above.)

●For malignant stenotic lesions, silicone stents can also be used but covered metallic stents are a reasonable option if only short-term use is planned (eg, 6 to 12 weeks). (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults", section on 'Airway stent'.)

●For benign tracheoesophageal fistulas (TEFs), silicone stents may be preferred when longer term use is needed, while in those with malignant TEF, covered self-expanding metal stents may be preferred for effective short-term palliation. (See "Tracheo- and broncho-esophageal fistulas in adults", section on 'Airway stent'.)

●For tracheobronchomalacia, silicone Y stents are preferred as a short-term trial to assess the potential success of tracheoplasty as well as for long-term symptomatic treatment if surgery is not feasible [57-59]. (See "Tracheomalacia in adults: Treatment and prognosis", section on 'Stent trial'.)

●For bronchial necrosis and dehiscence following lung transplantation, self-expanding uncovered metallic stents may promote neoepithelization and help close the airway defect [60]. (See "Airway complications after lung transplantation", section on 'Management'.)

●For patients with carinal disease, Y-shaped stents may be appropriate.

●For patients with a nonmalignant, complex airway stricture (stenosis involving two or more tracheal rings with mucosal and cartilaginous airway distortion, malacia, or collapse) from granulomatosis with polyangiitis, tuberculosis, or tracheobronchomalacia, custom-made stents may be required because such patients generally live with an indwelling airway stent for a prolonged duration (eg, >3 months).

Bronchoscopy — Most stents are placed bronchoscopically under direct visual guidance. While silicone stents require rigid bronchoscopy and general anesthesia, metal stents can be placed with a flexible bronchoscope using moderate sedation. (See "Flexible bronchoscopy in adults: Preparation, procedural technique, and complications" and "Flexible bronchoscopy in adults: Overview" and "Rigid bronchoscopy: Instrumentation" and "Anesthesia for adult bronchoscopy" and "Anesthesia for endotracheal stenting or repair of tracheoesophageal fistula".)

Adjunctive procedures — Insertion of an airway stent may be part of a bronchoscopic intervention (eg, dilation, cryosurgery, electrosurgery, or laser resection) or may be done days or weeks later as a palliative measure if the lesion recurs despite local intervention [61]. For example, if a benign stenotic lesion is not suitable for resection, dilation should be performed prior to stenting [39,47,62]. (See "Flexible bronchoscopy balloon dilation for nonmalignant airway strictures (bronchoplasty)".)

Technique of deployment — Most stents are placed bronchoscopically with or without fluoroscopic guidance. Some silicone stents can be placed using the grasping forceps of a rigid bronchoscope (movie 1), while others require special deployment techniques and devices supplied by the manufacturer. The technique is different for each type of stent. While some stents warrant preliminary dilation of the airway (eg, silicone stents), other stents self-expand (eg, self-expanding metal stent [SEMS]), thereby dilating the stenosis itself. Usually, stents are deployed directly into the stricture while in some cases, the stent is inserted into the distal component of the stricture and pulled up into the center of the stricture, assuring that the proximal and distal edges are satisfactorily treated.

For patients with obstructive lesions, identification of a critically narrowed airway segment (ie, the "choke point") is difficult to appreciate during bronchoscopy. Sequential multimodality assessment with spirometry, ultrathin bronchoscopy, and endobronchial ultrasound can be used to guide placement of an airway stent over the choke point, but this approach is technically difficult and experimental [63]. In addition, the choke point may migrate following stent placement, requiring revision or placement of a second stent.

Investigational techniques — Descriptions of stent placement using radiographic guidance have been reported. A retrospective study of carinal and pericarinal stent insertion placed over a guidewire with fluoroscopic assistance during bronchoscopy reported improvement in clinical symptoms in more than 90 percent of cases [64]. However, it was followed by the usual 30 percent incidence of stent-related complications. (See 'Complications' below.)

FOLLOW-UP — In the immediate postoperative period, patients are recovered from bronchoscopy in the usual fashion. Most patients can be discharged the same day unless the procedure is performed as an inpatient. (See "Flexible bronchoscopy in adults: Preparation, procedural technique, and complications", section on 'Postprocedure monitoring' and "Anesthesia for endotracheal stenting or repair of tracheoesophageal fistula", section on 'Extubation and recovery'.)

Immediate postoperative stent-related complications are unusual, although stent migration is a possibility for poorly fitting stents. During the next few days and weeks (typically six weeks) after stent placement, patients are monitored clinically for symptoms of relief (eg, improvement of dyspnea, reduced coughing). Patients do not routinely undergo imaging or pulmonary function testing but this can be done if symptoms recur. Any patient with an airway stent who develops new respiratory symptoms should undergo bronchoscopy to look for stent-related complications (table 3) [5].

The role of surveillance bronchoscopy and chest computed tomography two to three months after stent placement is controversial [65,66]. Some centers do not perform routine surveillance bronchoscopy or imaging because the yield in detecting major stent-related complications in asymptomatic individuals appears to be low, whereas other centers perform an initial follow-up bronchoscopy at approximately six weeks to assess for granulation tissue formation and mucostasis as these complications can be easier to manage when discovered earlier.

Steroids are not routinely administered to prevent granuloma formation and antibiotics are not routinely administered to prevent infection.

Despite the paucity of literature, many experts prescribe mucolytics or aerosolized saline to patients with indwelling stents.

Eventually, some stents are removed if they are no longer needed (eg, resolution of a benign process) or if complications occur. Stent removal is discussed separately. (See 'Removal' below.)

COMPLICATIONS — Complications are bronchoscopy- and stent-related.

Bronchoscopy-related — Complications of bronchoscopy are discussed separately. (See "Flexible bronchoscopy in adults: Preparation, procedural technique, and complications", section on 'Complications'.)

Stent-related — Most airway stents are initially well-tolerated. However, stent-related complications are common (up to one-third) (table 3) [67-69], although life-threatening complications are rare [70]. As an example, one study of 52 patients with stents placed for central airway obstruction, reported complications including migration (7.6 percent), tumor overgrowth (15 percent), infection (5.7 percent), granulation tissue formation (3.8 percent), and mucus plugs (3.8 percent). Rates of each complication vary depending upon the type of stent used and population in whom the stent is used [23,24].

Migration — Migration of the stent is more commonly encountered with silicone than metal stents (including covered metal stents). Migration is usually due to an inappropriately sized stent, violent coughing, resolution of the extrinsic compression that maintained the stent in position, and tumor growth. This can be both an early and late complication of stent placement. Stents can migrate proximally or distally. Migration proximally into the larynx may cause hoarseness, loss of voice, cough or dyspnea, and, rarely, airway obstruction. Migration distally may cause dyspnea, cough, and obstruction of a lobar bronchus to result in atelectasis or pneumonia; rarely life-threatening airway obstruction can occur due to bilateral main bronchial obstruction by a stent saddled horizontally on the carina. In most cases, the stent can be repositioned or an alternate stent can be placed (eg, longer or larger stent); in some cases the stent can be removed completely, if it is assessed that it is no longer indicated.

Granulation tissue or tumor infiltration — A local inflammatory reaction can be provoked by the stent, resulting in the growth of granulation tissue at the proximal and distal ends of the device (picture 11 and picture 8). This is mostly a late complication that occurs weeks to months after stent placement and is most problematic with uncovered metal stents where granulation tissue can also develop in between the interstices of the stent. Similarly, if the stent is placed for malignant lesions, tumor infiltration through the stent can also occur. If granulation or tumor infiltration is severe, stent obstruction may develop.

In most circumstances, granulation tissue resolves after removal of the stent. If the stent cannot be removed, it may be treated using local ablative therapies; however, in such cases the stent may need to be temporarily removed to avoid burning of the stent depending on the chosen ablative method. In some cases, when granulation is extensive, it may be impossible to remove the stent, in which case, granulation tissue can be removed using a forceps or the beveled edge of a rigid bronchoscope, cryotherapy or carefully administered thermal resection making sure to avoid supplemental oxygen to reduce the risk of airway fire. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults", section on 'Diagnostic evaluation and initial management'.)

It is uncertain if corticosteroids given at the time of stent placement diminish the inflammatory reaction [5].

Reduced mucociliary clearance — Stent obstruction may occur due to accumulated respiratory secretions [71]. This is an early or late complication of stent placement and is most problematic with long stents (eg, Y-shaped stents).

While most cases are minor and patients are able to expectorate phlegm, some cases of severe mucus impaction will need emergent bronchoscopy for pulmonary toilet.

Stent fracture — Stent fracture is a late complication that may be seen more commonly with metal stents and is an indication for removal since fractured wires may perforate the airway wall into vascular structures and become a nidus for granulation tissue formation.

Obstruction — Stent obstruction is an uncommon complication that can occur due to granulation tissue, tumor infiltration, or mucus impaction. It is treated by treating the underlying reason for obstruction.

Recurrent infection — Occasionally, patients experience recurrent lower respiratory tract inflammation or infection. This is an early and late complication of stent placement and is occasionally associated with halitosis. In cases of purulent secretions or persistent halitosis, secretions can be sampled and a trial of antibiotics given [71]. Colonization with pathogenic organisms including Staphylococcus, Streptococcus, and Klebsiella but without clinical signs of infection has been reported [72,73]. Bacterial colonization or infection may increase the risk of granulation tissue formation.

Airway and vascular perforation — Airway wall and vascular perforation can be seen following the placement of self-expanding metal stents. This may be offset by the proper selection of stent size (particularly maximal dilated diameter).

Stents, particularly self-expanding metal stents, can perforate the airway wall and migrate into the mediastinum, and perforate other structures including the esophagus or major blood vessels, although this is rare. It may be evident radiologically or bronchoscopically depending upon location and stent type (eg, silicone stents are not readily appreciated radiologically). A stent that has eroded through the airway wall warrants immediate evaluation with computed tomography and bronchoscopy and multidisciplinary consultation with interventional pulmonary and thoracic surgery experts. Stents may be removed bronchoscopically or may require a thoracotomy for surgical removal, depending upon their location. Stents eroding in to the esophagus may require endoscopy and subsequent treatment of the airway-esophageal fistula.

Stents may also erode into vascular structures. Patients with new or increasing hemoptysis, even if scant, should be suspected as having possible vascular erosion. Vascular erosion is life-threatening and requires urgent evaluation with surgical and radiological experts to decide on the optimal therapy.

Others — Other rare complications include the following:

●Metal fatigue (ie, decreased strength) can occur with time in patients with metal stents as a late complication.

●Fistulous communication with surrounding vascular and nonvascular structures can occur as a late complication.

REMOVAL — Stents that are no longer indicated or cause significant complications need to be removed and/or replaced. The removal process can be difficult, although silicone stents are more readily removed than metal stents. In an observational study conducted over 10 years, 58 percent of procedures to remove a metal stent had a complication [74]. The most common complication was reobstruction (46 percent), followed by post-procedure respiratory failure (33 percent), a mucosal tear (16 percent), and tension pneumothorax (2 percent).

As a general principle, the stent should be removed in one piece to lower the risk of leaving stent fragments. In addition, it is important to try to remove the proximal and distal granulation tissue before attempting to remove any stent, although some local ablation procedures risk burning the stent and causing airway fire. Choice of procedure to remove granulation tissue prior to stent removal is discussed above. (See 'Granulation tissue or tumor infiltration' above.)

Removal of silicone stents is generally performed using a rigid bronchoscope, although some experts use a flexible bronchoscope. The stent is grasped using a grasping forceps. Using a twist-and-pull maneuver (thought to prevent mucosal tearing), the stent may be pulled toward the barrel of the rigid bronchoscope. The entire apparatus is then removed from the airway with the stent constantly under direct view.

The removal of metal stents and hybrid stents in the first six weeks following placement is similar to the removal of silicone stents. However, after this period, removal is much more difficult and may require airway dilatation above and below the stent (eg, with a Fogarty balloon) as an attempt to separate the stent from the airway wall before device removal.

Some stents may have proximal sutures that can be pulled to "purse-string" the proximal end of the stent to facilitate removal.

SUMMARY AND RECOMMENDATIONS

●Airway stents are tube-shaped devices with a hollow lumen that are inserted into an airway bronchoscopically. (See 'Introduction' above.)

●Airway stenting is, in general, a palliative therapy or bridge to curative therapy for patients with benign or malignant disorders of the airway, most commonly, central airway obstruction (CAO) due to malignancy (table 1). Other indications include select patients with tracheal- or bronchial-esophageal fistula, tracheo- and tracheobronchomalacia, and anastomotic dehiscence following lung or heart-lung transplantation. In most cases, airway stenting results in the immediate improvement of symptoms as well as improvement in lung function, exercise capacity, and quality of life. (See 'Patient selection' above.)

●Contraindications to bronchoscopy, general anesthesia, and/or moderate sedation are also considered contraindications to airway stenting. Importantly, airway stenting is almost always performed after to thermal ablation (eg, laser therapy, electrocautery, argon plasma coagulation, or cryotherapy) of obstructing tissues because of a risk of stent obstruction and stent fracture, if thermal ablation is deployed close to the stent. (See 'Contraindications' above.)

●The main classes of stents are silicone stents, metal stents (covered or uncovered), and hybrid stents (metal covered with either silicone or polypropylene or other covering) (table 2 and picture 1). In general, silicone stents are most commonly used for nonmalignant disease since they are durable, suitable for long-term or indefinite use, easy to reposition and remove, and are cheaper. However, they tend to migrate and require rigid bronchoscopy for placement. While uncovered metal stents can be placed using a flexible bronchoscope and have excellent adherence properties with great expansile force, they are difficult to remove and serious complications such as airway perforation and stent obstruction due to tumor or granulation tissue regrowth through the interstices of the stent are common; these features have led to a Black Box warning issued by the US Food and Drug Administration to avoid their use in patients with benign lesions. Hybrid stents have mixed properties of silicone and metal stents and are being increasingly used. (See 'Types of stents' above.)

●Airway stents should only be placed by experts trained in their use. Choosing a stent depends upon the type, size, and location of lesion being treated, the anticipated duration of use, the patient’s preference, the cost, and the available expertise. When choosing a stent, the advantages and disadvantages of each stent should be taken into consideration (table 2). Each stent is unique and requires specific manufacturer instructions for deployment. (See 'Insertion technique' above.)

●Following stent placement, patients are monitored clinically for symptoms of relief (eg, improvement of dyspnea). For patients who develop new respiratory symptoms, most experts agree that bronchoscopy should be performed to look for stent-related complications (table 3), although some experts perform surveillance bronchoscopy for the advance detection of complications. Follow-up chest imaging and pulmonary function testing are not routine. (See 'Follow-up' above.)

●While most airway stents are initially well-tolerated, up to one-third of patients experience stent-related complications (table 3), although life-threatening complications are rare. Complications include granulomatous or tumor infiltration above, below, or through the stent, reduced mucociliary clearance, stent migration, recurrent infection, and, rarely, airway perforation, stent fracture, metal fatigue, and fistulous communication with surrounding vascular and nonvascular structures. (See 'Complications' above.)

●Stents that are no longer indicated or cause significant complications need to be removed or replaced. In general, silicone stents are more readily removed than metal ones. Removal can be fraught with complications, including mucosal tears and stent fragmentation. (See 'Removal' above.)