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(Radiology. 1999;213:905-912.)
© RSNA, 1999

Technical Developments

Tracheobronchial Strictures: Treatment with a Polyurethane-covered Retrievable Expandable Nitinol Stent-Initial Experience1

Ho-Young Song, MD, Tae Sun Shim, MD, Sung-Gwon Kang, MD, Gyoo-Sik Jung, MD, Do Yun Lee, MD, Tae-Hyung Kim, BS, Sangsoo Park, PhD, Young Moo Ahn, PhD and Woo Sung Kim, MD

1 From the Depts of Diagnostic Radiology (H.Y.S., S.G.K.), Internal Medicine (T.S.S., W.S.K.), and Biomedical Engineering (T.H.K., S.P.), Asan Medical Center, University of Ulsan College of Medicine, 388-1 Poongnap-Dong, Songpa-Ku, Seoul 138-736, Korea; Dept of Clothing and Textiles, Hansung University, Seoul, Korea (Y.M.A.); Dept of Diagnostic Radiology, College of Medicine, Kosin University, Pusan, Korea (G.S.J.); and Dept of Diagnostic Radiology, Yonsei University College of Medicine, Seoul, Korea (D.Y.L.). From the 1998 RSNA scientific assembly. Received Dec 1, 1998; revision requested Jan 14, 1999; revision received Feb 19; accepted Jun 8. Supported in part by grant HMP-98-G-2-043 from the Highly Advanced National Project, Ministry of Health and Welfare, Republic of Korea. Address reprint requests to H.Y.S. (e-mail: hysong@www.amc.seoul.kr).


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
A polyurethane-covered retrievable expandable stent was placed in 13 patients with tracheobronchial strictures. In four patients with benign strictures, the stent was removed with use of a retrieval hook 2–6 months after placement. After stent removal, three of the four patients did not need further treatment. The retrievable stent warrants further investigation in the treatment of tracheobronchial strictures.

Index terms: Bronchi, diseases, 671.1493 • Bronchi, stenosis or obstruction, 671.3239 • Stents and prostheses, 671.1299 • Trachea, diseases, 671.1493 • Trachea, stenosis or obstruction, 671.3239


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Fluoroscopically guided placement of noncovered or covered self-expandable metallic stents is a relatively new method of treating malignant and benign tracheobronchial strictures. Although no large controlled trials have been performed, to our knowledge, published data suggest that the procedure is a safe and easy nonsurgical treatment in cases of inoperable tracheobronchial strictures with resultant dyspnea (1–16). In addition, the procedure may reduce the considerable morbidity and complication rates associated with conventional silicone tube insertion (1,10,14). However, complications such as migration, fracture of the metallic mesh, blockage, tumor ingrowth, and formation of granulation tissue occurred in some cases during and after the procedure (1,2,14,17). Some of these complications, such as delayed migration, fracture of the stent, and formation of granulation tissue, could be avoided with use of a retrievable and covered stent as in esophageal strictures (18).

Recently, a noncovered expandable metallic stent was used in the treatment of tracheobronchial strictures (n = 8) or tracheobronchomalacia (n = 8) in 16 infants and children (15). The stent was removed in six of eight cases with tracheobronchomalacia and in one of eight cases with tracheobronchial strictures 6–44 months after stent placement. All patients were reported to be well with no recurrence after removal of the stent. Removal of the stent, however, was difficult and general anesthesia was needed because the stent design was not optimized for removal. Moreover, one patient died at attempted removal because the stent was tightly bound into the tracheal wall by an inflammatory reaction (15).

To make the stent removable and more tolerable, we designed a polyurethane-covered retrievable expandable nitinol stent and a device for removal of the stent. The purpose of this study was to evaluate placement and removal of this stent.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Indications for Stent Placement
From September 1997 to October 1998, 13 consecutive patients (eight men and five women; age range, 36–68 years; mean age, 56 years) with dyspnea caused by tracheobronchial strictures (n = 12) or tracheobronchomalacia (n = 1) were treated by means of fluoroscopically guided placement of a covered retrievable expandable nitinol stent. Among the 13 patients, eight had a malignant stricture that was deemed unsuitable for surgical management, four had a benign stricture refractory to balloon dilation, and one had tracheobronchomalacia. The underlying malignancies were recurrent carcinoma of the lung or trachea after surgery or radiation therapy in three patients and recurrent carcinoma of the esophagus or stomach in five (Table). In one of the eight patients with a malignant stricture (patient 8), rapidly proliferating granulomatous inflammatory reaction developed after endobronchial radiation therapy for recurrent bronchogenic cancer, which was not controlled with repeated endoscopic resection. Further endoscopic resection was not attempted in the patient because of friability.


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  		Data from 13 Patients with Tracheobronchial Stent Placement
 
The causes of benign strictures were tracheostomy in three patients, tracheobronchomalacia after repair of a postintubation tracheal stricture in one, and endotracheal tuberculosis in one. The site of stricture was at the trachea in six patients, at the left main bronchus in five, and at the lower trachea straddling the left main bronchus in two. In patients with a benign stricture, balloon dilation was not effective because of frequent recurrences within 2 weeks after dilation. A total of 21 stents were placed in 19 procedures in 13 patients. More than one stent was necessary in five cases at either the initial or subsequent session because both the trachea and bronchi were involved, the stent had migrated, or the stricture recurred after the stent was removed. The diagnosis was established by means of review of history, computed tomographic (CT), and endoscopic biopsy findings. Informed consent was obtained from each patient, and this pilot study was approved by our university committee.

Stent Construction
The stent was woven 16 times from a single thread of 0.2-mm-diameter nitinol wire filament in a tubular configuration. The stent has 16 bent points on the upper and lower end portions. The wire filament crossed spirally in an unengaged manner. One segment of the wire filament ran alternately on and under other segments, which were arranged in a direction opposite to that of the segment, so that a number of meshes were formed by the crossing points of the segments. To prevent mucosal hyperplasia or tumor ingrowth through the stent wires, the stent was covered by being dipped in 12% polyurethane solution (Chronoflex; Cardiotech International, Woburn, Mass). To provide a firmer covering on the most proximal and distal parts of the stent, those areas were covered with 100% nylon mesh and then dipped in the polyurethane. The tracheal stent (Fig 1) was 16 or 20 mm in diameter when fully expanded and 40–50 mm long, and the bronchial stent was 10 or 12 mm in diameter and 30–40 mm long. In two cases, a hinged stent was placed in the bifurcation area so that a tracheal stent was placed in the lower trachea and a bronchial stent was placed in the left main bronchus. To make a hinged stent, the ends of a tracheal stent and a bronchial stent were connected at one point without overlap by using nylon monofilament. A radiopaque marker was attached at the hinged portion. The radiopaque marker was made by tying a 0.3-mm gold wire six times round the hinged portion.



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  		Figure 1. Top to bottom: Covered retrievable nitinol stent, stent introducer set (guide wire, guiding balloon catheter, breathing tube, compressed stent, pusher catheter, and sheath), stent retrieval set (guide wire, dilator, and sheath), and hook wire.

 
To make the stent removable, a drawstring made of nylon monofilament was attached to the upper inner margin of the stent (Fig 2). A nylon loop (2 mm in diameter) was hooked inside to each bend of the proximal end of the stent and secured with suture. Another nylon thread was passed through each of the nylon loops to form a larger loop (a drawstring) that filled the circumference of the inside of the stent. The resultant loop was tied up. The stent was constructed by us in our research laboratory. A stent, at least 10 mm longer than the stricture, was selected for placement so that the proximal and distal parts of the stent would rest on the upper and lower margins of the stricture, respectively. Regarding the diameter of the tracheal stent, a 20-mm stent was selected for the male patients and a 16-mm stent for the female patients. Regarding the diameter of the bronchial stent, a 12-mm stent was selected for the male patients and a 10-mm stent for the female patients.



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  		Figure 2. Diagrams show two drawstrings attached to the upper inner margin of the stent. 1 = central lumen, 2 = drawstrings, 3 = nylon loop, 4 = upper margin of the wire.

 
Stent Introducer Set and Retrieval Set
A tracheal stent introducer set consists of an 8-mm sheath, a 4-mm breathing tube, a pusher catheter, and a guiding balloon catheter 8 mm in diameter and 3 cm long (Medi-tech/Boston Scientific, Watertown, Mass). The sheath, breathing tube, and pusher catheter were constructed by a local manufacturer (Stentech, Seoul, Korea) to our specifications. A deflated balloon catheter was passed through a breathing tube, and then both were passed through a pusher catheter. These three were pushed into the sheath, with half of the balloon out of the sheath. From the opposite end, a stent was passed over the balloon catheter and breathing tube and then compressed to be loaded between the breathing tube and the distal end of the sheath.

The stent retrieval set (Fig 1) consists of a 13-F sheath, a 10-F dilator, a hook wire, and a 0.035-inch guide wire (Terumo, Tokyo, Japan). The sheath and dilator were constructed by a local manufacturer (Stentech) to our specifications, and the hook wire was constructed by us in our research laboratory with use of a nitinol wire. The end of the hook wire was constructed in a question mark configuration to hook the drawstring of the stent. The distal 20-mm section of the question mark portion was positioned at an angle of about 30° to the axis. An additional bend was made in this section with the use of pliers so that the hook would not catch the end of the sheath when the hook was being withdrawn.

Tracheal Stent Placement Technique
The site, severity, and length of the stricture were evaluated before stent placement by means of conventional radiography, CT, bronchoscopy, and respiratory function studies (spirometry and arterial blood gas analysis). Topical anesthesia of the pharynx and larynx was routinely achieved with an aerosol spray before the procedure. Prophylactic antibiotics and steroids were not used. Drugs for sedation were routinely used. With bronchoscopic guidance, a 0.035-inch exchange guide wire (Terumo) was inserted through the mouth across the stricture into the distal portion of the trachea or bronchus. A straight 5-F graduated sizing catheter (Cook, Bloomington, Ind) was passed over the guide wire to the distal part of the stricture to measure the length of the stricture. With fluoroscopic guidance, the location of the narrowed tracheobronchial lumen was marked on the patient's skin. When a stricture was not well defined at fluoroscopy, the guide wire was removed from the catheter and a small amount of diluted nonionic contrast medium (Ultravist 300; Schering-Korea, Ansung, Korea) was injected through the catheter to opacify the narrowed lumen, and then the length of the stricture was measured. An angioplasty balloon catheter (3–4 cm long and 10 mm in diameter) was passed over the guide wire to a position over the stricture. The balloon was slowly inflated with a diluted water-soluble contrast medium until the "hourglass deformity" created by the stricture disappeared from the balloon contour. The 0.035-inch exchange guide wire was changed to a super stiff J tip guide wire (Medi-tech/Boston Scientific), and the balloon was removed with the guide wire left in the trachea.

The proximal part of the stent was lubricated with a water-soluble lubricant (Chlorhexidine cream; Tongsan, Ansan, Korea). The stent was then compressed and loaded into the introducer set. The patient was placed in the right anterior oblique or supine position with the neck extended. With fluoroscopic guidance, the whole introducer set was passed over the guide wire into the trachea and advanced until the distal tip of the stent reached approximately 1 cm beyond the stricture (Fig 3). Then, the guiding balloon catheter was deflated, and the balloon catheter and the guide wire were removed. The pusher catheter was held in place (H.Y.S., G.S.J., S.G.K., D.Y.L.) with one hand while the sheath was slowly withdrawn in a continuous motion with the other hand. This freed the stent and allowed it to lie within the stricture and expand. Just after the sheath, the pusher catheter, and the breathing tube were removed, conventional radiography was performed to verify the position of the stent.



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  		Figure 3. A-E, Diagrams show the technical steps in tracheal stent placement. A, Insertion of a guide wire into the bronchus. B, Dilation of the stricture with use of a balloon catheter. C, Passage of an introducer set through the stricture. D, Withdrawal of the sheath over the pusher catheter. E, Expansion of the stent in the trachea.

 
In the patient with an endotracheal tube for tracheobronchomalacia, balloon dilation was not needed before stent placement, and stent placement was performed through the endotracheal tube by using the coaxial sheath technique.

Bronchial Stent Placement Technique
Topical anesthesia of the pharynx and larynx and balloon dilation of the stricture were performed with the same technique used for tracheal stent placement. With fluoroscopic guidance, a 14-F sheath with a dilator (Cook) was passed over the guide wire into the bronchus and was advanced until the distal tip of the sheath reached 1 cm beyond the stricture. Then, the dilator and the guide wire were removed from the sheath. After that, a stent was compressed and loaded into the sheath and then positioned within the bronchus with use of a pusher catheter. A hinged stent was placed into the distal trachea and left mainstem bronchus so the hinge would be located along the lateral aspect of the airway at the junction of the trachea and main bronchus as described previously (14).

Stent Removal Technique
We removed the stent in patients with a benign or malignant stricture when complications such as severe pain or migration occurred. In patients with a benign stricture with no complications, we routinely removed the stent 8 weeks after placement. After topical anesthesia of the larynx, a 0.035-inch guide wire (Terumo) was introduced through the mouth and then across the stent into the distal trachea or bronchus. A sheath with a dilator was passed down over the guide wire into the proximal stent lumen (Fig 4). After the dilator was removed from the sheath, a hook wire was introduced into the sheath and was advanced until the hook was passed through the sheath into the stent lumen. Then the sheath with the hook was pulled out of the stent so that the hook grasped the drawstring. When this happened, the hook wire was withdrawn through the sheath to collapse the proximal stent when it reached the sheath tip. The sheath, the hook wire, and the stent were then pulled out of the trachea.



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  		Figure 4. A-D, Diagrams show the technical steps in removal of the stent. A, Insertion of a sheath by using a dilator. B, Insertion of a hook wire into the sheath. C, Grasping of the drawstrings with the hook wire. D, Withdrawal of the hook wire through the sheath.

 
Follow-up
All patients underwent conventional radiography 1–3 days after stent placement to verify the state of expansion and position of the stent. In the first four patients, respiratory function studies (spirometry and arterial blood gas testing) were performed 1 day before and 3 days after stent placement. Bronchoscopy was performed when the follow-up conventional radiographs showed full expansion of the stent to verify patency of the stent.

In patients with a malignant stricture, clinical examination and conventional radiography were performed every 2 months after stent placement to detect stent migration. Follow-up bronchoscopy was performed only in patients with recurrent dyspnea or coughing. When clinical examination and conventional radiography were not practical because the patients were severely ill, then the patients or their families were contacted by telephone every 2 months for as long as the patients were alive. Information concerning coughing, pain, and dyspnea was obtained.

In patients with a benign stricture, conventional radiography and bronchoscopy were performed to evaluate patency of the stent every 2 weeks after the first bronchoscopic examination until the stent was removed. Clinical examinations and conventional radiography were also performed at 1 month, 3 months, and 12 months after removal of the stent to assess for recurrence. Follow-up bronchoscopy was performed 3 months after stent removal. After that, the patients were advised to visit our outpatient clinic if symptoms recurred, and all patients were contacted by telephone every 6 months.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Stent Placement
Stent placement was technically successful and well tolerated in all but two patients (patients 6 and 13). Patient 6, with tracheobronchomalacia involving the lower trachea and left main bronchus, had a very short trachea. First, we placed one stent through the endotracheal tube into the left main bronchus and then another stent into the lower trachea, but the tracheal stent migrated upward immediately after deployment. A second tracheal stent was placed through the first stent, but the second also migrated upward immediately after deployment. The two tracheal stents with upward migration and the bronchial stent were removed 1 week after they were placed, and a hinged stent was successfully placed with no further migration. The stent was removed less than 1 week later.

In patient 13, a hinged stent was placed lower than normal so that the distal part of the tracheal stent occluded the right main bronchus. The hinged stent was then relocated successfully by using bronchoscopic biopsy forceps with bronchoscopic and fluoroscopic guidance (Fig 5). To relocate the hinged stent, the drawstring was grasped with the forceps and pulled upward until the distal end of the stent reached just proximal to the orifice of the right main bronchus.



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  		Figure 5. Patient 13. (a) Left anterior oblique esophagogram obtained before stent placement shows a large fistula (black arrow) between the intrathoracic stomach (arrowheads) and the lower trachea (white arrows). (b) Anteroposterior conventional radiograph obtained during relocation of an incorrectly placed hinged stent by using endoscopic forceps (curved arrow) shows the distal end of the tracheal stent positioned in the left main bronchus (straight arrow). Notice the radiopaque marker at the hinged portion (arrowhead). (c) Anteroposterior conventional radiograph obtained after relocation of the incorrectly placed stent shows the stent (arrow) positioned properly. (d) Left anterior oblique esophagogram obtained 3 days after relocation of the stent shows occlusion (arrow) of the fistula.

 


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  		Figure 5. Patient 13. (a) Left anterior oblique esophagogram obtained before stent placement shows a large fistula (black arrow) between the intrathoracic stomach (arrowheads) and the lower trachea (white arrows). (b) Anteroposterior conventional radiograph obtained during relocation of an incorrectly placed hinged stent by using endoscopic forceps (curved arrow) shows the distal end of the tracheal stent positioned in the left main bronchus (straight arrow). Notice the radiopaque marker at the hinged portion (arrowhead). (c) Anteroposterior conventional radiograph obtained after relocation of the incorrectly placed stent shows the stent (arrow) positioned properly. (d) Left anterior oblique esophagogram obtained 3 days after relocation of the stent shows occlusion (arrow) of the fistula.

 


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  		Figure 5. Patient 13. (a) Left anterior oblique esophagogram obtained before stent placement shows a large fistula (black arrow) between the intrathoracic stomach (arrowheads) and the lower trachea (white arrows). (b) Anteroposterior conventional radiograph obtained during relocation of an incorrectly placed hinged stent by using endoscopic forceps (curved arrow) shows the distal end of the tracheal stent positioned in the left main bronchus (straight arrow). Notice the radiopaque marker at the hinged portion (arrowhead). (c) Anteroposterior conventional radiograph obtained after relocation of the incorrectly placed stent shows the stent (arrow) positioned properly. (d) Left anterior oblique esophagogram obtained 3 days after relocation of the stent shows occlusion (arrow) of the fistula.

 


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  		Figure 5. Patient 13. (a) Left anterior oblique esophagogram obtained before stent placement shows a large fistula (black arrow) between the intrathoracic stomach (arrowheads) and the lower trachea (white arrows). (b) Anteroposterior conventional radiograph obtained during relocation of an incorrectly placed hinged stent by using endoscopic forceps (curved arrow) shows the distal end of the tracheal stent positioned in the left main bronchus (straight arrow). Notice the radiopaque marker at the hinged portion (arrowhead). (c) Anteroposterior conventional radiograph obtained after relocation of the incorrectly placed stent shows the stent (arrow) positioned properly. (d) Left anterior oblique esophagogram obtained 3 days after relocation of the stent shows occlusion (arrow) of the fistula.

 
Clinical improvement was obtained after successful stent placement in all patients. Bronchoscopy performed after full expansion of the stent showed the lumen with the stent remained patent. In patients with esophagorespiratory fistula, the stent sealed off the fistula with consequent improvement in respiratory and nutritional status. Most patients with tracheal stents felt dull chest pain for 1–3 days after placement, but no patient with a bronchial stent did.

Stent Removal
Downward migration of a 16-mm-diameter stent occurred in one patient (patient 4) during bronchoscopy performed 1 week after stent placement. The migrated stent was removed with use of a stent retrieval set. This patient underwent placement of a 20-mm-diameter stent because dyspnea recurred 10 days after the stent was removed. In the other three patients (patients 1–3) with a benign stricture, the stent was also removed 2 months after stent placement. In patient 6, the stent was not removed because of tracheobronchomalacia. Removal of the stent was well tolerated in all patients. The stents of two of the four patients who underwent stent removal were blood stained, and bronchoscopy showed a small amount of mucosal bleeding, but bleeding stopped spontaneously within 3 minutes of removal.

Follow-up
During the follow-up period, four of the eight patients with a malignant stricture died (range, 1–16 weeks; mean, 6 weeks) after stent placement owing to hemoptysis (patient 8) or diffuse metastasis of the underlying cancer. The remaining four patients with a malignant stricture were alive 3–24 weeks (mean, 11 weeks) after stent placement. In patient 8, with radiation-induced edema and inflammation, bronchoscopy was performed 7 days after stent placement. The tumor bled when the fiberscope touched the stent during bronchoscopy. The patient died of massive hemoptysis from the tumor 5 hours after the bronchoscopic examination.

All four patients with a benign stricture and one patient with tracheobronchomalacia were alive at the time this article was written. The four patients with a benign stricture whose stents were removed at 7 days or 2 months after stent placement were followed up for a mean 47 weeks (range, 45–49 weeks) after the stent was removed. The initial improvement rate in the four patients was 100%, but only one (patient 3) maintained the initial improvement during the follow-up and did not need further treatment. Symptoms recurred in the remaining three patients within 3 weeks after stent removal. Among these three patients, a second stent was placed and removed 6 months later in two patients (patients 2 and 4). In the other patient (patient 1), the stent was not removed because the patient was reluctant to undergo stent removal in the absence of respiratory symptoms. The former were free of symptoms for 22 and 19 weeks, respectively, at the time of this writing (Fig 6).



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  		Figure 6. Patient 4. (a) Anteroposterior conventional radiograph obtained during stent placement shows a tracheal stent introducer set (arrowheads) passing over the stricture (arrows). (b) Anteroposterior conventional radiograph obtained immediately after stent placement shows a stent not fully expanded (arrow). (c) Right anterior oblique conventional radiograph obtained during removal of the stent 6 months after placement shows a hook (arrow) within the stent lumen. (d) Right anterior oblique conventional radiograph obtained while pulling the hook (solid arrow) out of the trachea shows the collapsed portion (open arrow) of the stent.

 


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  		Figure 6. Patient 4. (a) Anteroposterior conventional radiograph obtained during stent placement shows a tracheal stent introducer set (arrowheads) passing over the stricture (arrows). (b) Anteroposterior conventional radiograph obtained immediately after stent placement shows a stent not fully expanded (arrow). (c) Right anterior oblique conventional radiograph obtained during removal of the stent 6 months after placement shows a hook (arrow) within the stent lumen. (d) Right anterior oblique conventional radiograph obtained while pulling the hook (solid arrow) out of the trachea shows the collapsed portion (open arrow) of the stent.

 


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  		Figure 6. Patient 4. (a) Anteroposterior conventional radiograph obtained during stent placement shows a tracheal stent introducer set (arrowheads) passing over the stricture (arrows). (b) Anteroposterior conventional radiograph obtained immediately after stent placement shows a stent not fully expanded (arrow). (c) Right anterior oblique conventional radiograph obtained during removal of the stent 6 months after placement shows a hook (arrow) within the stent lumen. (d) Right anterior oblique conventional radiograph obtained while pulling the hook (solid arrow) out of the trachea shows the collapsed portion (open arrow) of the stent.

 


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  		Figure 6. Patient 4. (a) Anteroposterior conventional radiograph obtained during stent placement shows a tracheal stent introducer set (arrowheads) passing over the stricture (arrows). (b) Anteroposterior conventional radiograph obtained immediately after stent placement shows a stent not fully expanded (arrow). (c) Right anterior oblique conventional radiograph obtained during removal of the stent 6 months after placement shows a hook (arrow) within the stent lumen. (d) Right anterior oblique conventional radiograph obtained while pulling the hook (solid arrow) out of the trachea shows the collapsed portion (open arrow) of the stent.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Obstruction of the large airways by either benign or malignant processes is associated with high morbidity and possible early death by asphyxia (14). Treatment of serious airway obstruction in patients in whom surgery is contraindicated is often a challenge (15). Recently, different kinds of covered and noncovered expandable metallic stents have been used successfully in patients with tracheobronchomalacia, noninflammatory strictures, and intra- or extraluminal tumor to relieve dyspnea or to occlude esophagorespiratory fistulas (1–16). The expandable metallic stents were found to overcome some of the limitations of nonexpandable silicone stents (1,10,14). Implantation of the former is better tolerated and safer than that of the latter because the expandable stents can be implanted by using a thin delivery system. They should create a larger airway as they are less bulky and have greater expansile properties than their silicone rubber counterparts. They also may be associated with superior mucociliary clearance as only a small area of mucosa is covered by the stent, and the metal lattice becomes overgrown by ciliated respiratory epithelium (1,7,10).

The use of noncovered expandable metallic stents has some limitations, however, not only because the noncovered stents are not suitable for the treatment of esophagorespiratory fistula but also because mucosal hyperplasia or progressive tumor ingrowth through the openings between the wire filaments of the noncovered stents tends to cause progressive dyspnea (10,12). In addition, overall complication rates of 13%–22% have been reported in studies (1,2,10,14) that have included more than six and fewer than 55 patients. Rousseau and coworkers (1) reported that the Gianturco stent led to a complication rate as high as 31% in 19 patients. To overcome the limitations of noncovered expandable metallic stents, George et al (10) used a totally covered Gianturco stent and Kishi et al (11) and Miyayama et al (12) used a partially covered Gianturco stent in patients with a malignant tracheobronchial stricture. The covered stents are not widely accepted, however, because of migration and their inability to be removed (10). To make the stent removable, we designed a polyurethane-covered retrievable expandable nitinol stent and a device to remove that stent.

We agree that it would be ideal to remove a stent after it is no longer needed because foreign material has been inserted into the airway (15). Our therapeutic plan in patients with a benign stricture was to leave the stent in place for 8 weeks. Filler and coworkers (15) suggested a stent be left in place for 1 year in children with tracheomalacia as an optimal period after which normal airway growth would decrease the likelihood of complete airway collapse at stent removal. In our opinion, a tracheobronchial stent should remain in patients with a benign stricture until the stricture has healed. We are not certain about the best time to remove a stent because it will be different in each case according to the causes, duration, and severity of the strictures. When we removed a stent 1 week to 2 months after placement in four patients with a benign stricture, symptoms recurred in three within 3 weeks. All three patients experienced tracheal stenosis in less than 2 months, and a second stent was placed and removed 6 months later. Interestingly, symptoms had not recurred in two of these three patients at the time of this writing.

The polyurethane-covered retrievable expandable nitinol stent has several advantages over the conventional noncovered expandable metallic stent. There is little chance of tumor ingrowth in patients with a malignant stricture because the stent is covered by a polyurethane membrane. Fracture of the stent is unlikely because the stent is woven from a single thread of nitinol wire. The stent can be easily relocated if placed incorrectly. The stent also can be easily removed if it causes complications. Placement of a retrievable stent can extend the indications to patients with a benign stricture whose lesions were previously considered very difficult to treat if not untreatable. The covered stent, however, has important limitations. Insertion of a covered stent within the distal bronchial tree may occlude an orifice to an upper lobe, whereas placement at the level of the main carina may lead to obstruction of a main bronchus. In conclusion, although further clinical trials and extended follow-up studies are needed, our preliminary results indicate that a covered retrievable expandable nitinol stent warrants further investigation in the palliative treatment of benign and malignant tracheobronchial strictures.


   Footnotes
 
Author contributions: Guarantor of integrity of entire study, H.Y.S.; study concepts, H.Y.S., W.S.K.; study design, H.Y.S., T.S.S., S.G.K.; definition of intellectual content, T.S.S., S.P.; literature research, G.S.J., T.Y.K., Y.M.A.; clinical studies, H.Y.S., T.S.S., W.S.K., G.S.J., S.G.K., D.Y.L.; experimental studies, T.H.K., S.P., Y.M.A.; data acquisition, S.P., Y.M.A.; data analysis, S.G.K., D.Y.L.; manuscript preparation, H.Y.S.; manuscript editing, H.Y.S., T.S.S.; manuscript review, T.S.S., W.S.K., G.S.J., S.G.K., D.Y.L., S.P., Y.M.A.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Rousseau H, Dahan M, Lauque D, et al. Self-expandable prostheses in the tracheobronchial tree. Radiology 1993; 188:199-203.[Abstract/Free Full Text]
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  3. Varela AV, Maynar M, Irving D, et al. Use of Gianturco self-expandable stents in the tracheobronchial tree. Ann Thorac Surg 1990; 49:806-809.[Abstract]
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