- Email: [email protected]
Treatment of Tracheobronchial Obstruction with a Polytetrafluoroethylene-covered Retrievable Expandable Nitinol Stent
Treatment of Tracheobronchial Obstruction with a Polytetrafluoroethylene-covered Retrievable Expandable Nitinol Stent Ji Hoon Shin, MD, Ho-Young Song, MD, Gi Young Ko, MD, Tae-Sun Shim, MD, Sang Wee Kim, MD, Young Kwon Cho, MD, Heung-Kyu Ko, MD, Yong Jae Kim, MD, Hyun-Ki Yoon, MD, and Kyu-Bo Sung, MD
PURPOSE: To evaluate the clinical effectiveness of polytetrafluoroethylene (PTFE)– covered retrievable expandable nitinol stents in tracheobronchial strictures. MATERIALS AND METHODS: With fluoroscopic guidance, PTFE-covered retrievable expandable nitinol stents were placed in 15 symptomatic patients with benign (n ⴝ 6) or malignant (n ⴝ 9) tracheobronchial strictures. Complications and improvement in respiratory status were evaluated. Stents were removed electively 6 months after placement in benign strictures or if complications occurred. Membrane degradation or separation from the wire mesh was evaluated in removed stents. RESULTS: A total of 17 stents were successfully placed and were well tolerated in all patients. Sputum retention, stent migration, and tissue hyperplasia occurred in 23.5% (n ⴝ 4), 17.6% (n ⴝ 3), and 17.6% (n ⴝ 3) of stents, respectively. A total of 11 stents were successfully removed electively 6 months after placement (n ⴝ 4) or when complications occurred (n ⴝ 7). All 11 such stents were removed without difficulty with use of standard techniques, antecedent balloon dilation being necessary in two cases as a result of tissue hyperplasia. No removed stent showed signs of membrane degradation, and two removed stents showed signs of membrane separation from the mesh. CONCLUSIONS: PTFE-covered retrievable expandable nitinol stents were effective in the treatment of tracheobronchial strictures. Stent removal was easy with use of standard techniques, and no removed stent showed evidence of membrane degradation. J Vasc Interv Radiol 2006; 17:657– 663 Abbreviation:
PTFE ⫽ polytetrafluoroethylene
LARGE airway obstruction from benign or malignant causes is associated with high morbidity rates and possible early death. Recently, several investigators (1–7) have used covered expandable metallic stents as a relatively new method for the treatment of airway obstructions. Covered stents are From the Department of Radiology and the Research Institute of Radiology (J.H.S., H.Y.S., G.Y.K., Y.K.C., H.K.K., Y.J.K., H.K.Y., K.B.S.) and Department of Internal Medicine (T.S.S., S.W.K.), University of Ulsan College of Medicine, Asan Medical Center, 388-1, Pungnap-2dong, Songpa-gu, Seoul, 138-736, Korea. Received September 12, 2005; accepted December 25. Address correspondence to H.Y.S.; Email: [email protected] None of the authors have identified a conflict of interest. © SIR, 2006 DOI: 10.1097/01.RVI.0000203803.98007.9F
associated with relatively little hyperplastic tissue ingrowth and can be removed electively or in cases of complications unless the membrane is disrupted (1,4,5,8,9). Several recent reports (4,5,9) have specifically highlighted the importance of covered stent removal in patients with benign airway strictures. Polyurethane has been widely used to cover expandable metallic stents for the airway and esophagus, gastrointestinal tract, biliary tract, and urethra (1,2,4,5,9 –14). However, polyurethane degradation has been reported when such stents were inserted in the airway, biliary tract, and upper gastrointestinal tract for long periods of time (4,9,11,14). Those reports suggested that respiratory secretions or gastric juices are capable of damaging or perforating polyurethane membranes,
and they found that removal of stents with damaged membranes was difficult as a result of hyperplastic tissue ingrowth through perforations. To overcome shortcomings associated with polyurethane-covered stents, we designed retrievable expandable metallic stents covered with polytetrafluoroethylene (PTFE), which is a strong chemical-resistant material. The present study evaluated the clinical effectiveness of PTFE-covered retrievable expandable nitinol stents in patients with tracheobronchial strictures.
MATERIALS AND METHODS Patients From October 2003 to March 2005, 15 consecutive patients (10 male and five female; age range, 2– 68 years;
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PTFE-Covered Retrievable Expandable Nitinol Stent Placement in 15 Patients Stent Size Patient Age No. (y) Sex
Cause
Location of Strictures
Hugh-Jones Grade
Diameter Length (mm) (cm)
Before
After
Complications
1 2 3
25 36 38
M M F
Traumatic Tuberculous Tuberculous
Left main bronchus Left main bronchus Left main bronchus
12 12 10
4 3 4
III III III
I I II
4
53
F
After intubation
Trachea
16
5
V
III
5 6 7
36 22 2
F F F
Left main bronchus Left main bronchus Trachea
16 12 12 10
6 5 4 3
III II IV III Ventilated state
8
64
M
4
III
II
None
54
M
Left main and lowerlimb bronchus Left main bronchus
12
9
12
4
IV
IV
Sputum retention
10
68
M
Trachea
20
5
IV
II
Sputum retention
11 12
54 62
M M
Tuberculous Tuberculous Mediastinal primitive embryonal sarcoma Non–small-cell lung cancer Non–small-cell lung cancer Non–small-cell lung cancer Esophageal cancer Non–small-cell lung cancer
None Tissue hyperplasia Stent migration (proximal) Stent migration (proximal) Tissue hyperplasia Tissue hyperplasia None None
Trachea Trachea
20 20
6 6
IV V
III III
13 14
33 50
M M
9 9 5
V IV
III II
62
M
Trachea Left main and lowerlobe bronchus Trachea
20 20 12
15
Esophageal cancer Non–small-cell lung cancer Esophageal cancer
Sputum retention Stent migration (distal) Sputum retention None None
20
8
IV
II
None
mean age, 44 y) with tracheobronchial obstructions underwent fluoroscopically guided placement of PTFE-covered retrievable expandable nitinol stents. Our institution does not require institutional review board approval for retrospective reviews of patient records or images. The causes of the tracheobronchial obstructions were benign in six patients (tuberculous stricture, n ⫽ 4; traumatic bronchial stricture, n ⫽ 1; stenosis after intubation, n ⫽ 1) and malignant in nine patients (non–small cell-lung cancer, n ⫽ 5; esophageal cancer, n ⫽ 3; mediastinal primitive embryonal sarcoma, n ⫽ 1) (Table). The diagnosis of traumatic bronchial stricture and stenosis after intubation was made by bronchoscopy and computed tomography (CT) on the basis of relevant clinical histories. The diagnosis of other diseases was established by bronchoscopic or percutaneous biopsy. The obstruction sites were at the trachea (n ⫽ 7), left main bronchus (n ⫽ 6), and left main/lower bronchus (n ⫽ 2). Three patients with esophageal cancer reported dyspnea resulting
from tracheal invasion secondary to esophageal cancer, and one such patient (patient 13) already had an esophageal stent that had been placed 3 months previously. In five of the six patients with benign obstruction, the PTFE-covered stents were used as a result of failure of previous balloon dilation (n ⫽ 5) and/or polyurethane-covered stent placement (n ⫽ 4), whereas PTFE-covered stents were used in the primary treatment of the nine malignant obstructions and one near-complete benign obstruction (patient 2). One child with mediastinal primitive embryonal sarcoma (patient 7) was in a mechanically ventilated state, whereas the remaining 14 patients, all of whom were adults, had resting or exertional dyspnea. The Hugh-Jones classification was used to evaluate improvement in respiratory function before and 1 month after stent placement in the 14 adult patients but not in the child, who required ventilation. This classification is a five-grade system used to assess breathlessness on the basis of daily ac-
tivities, with grade V indicating the most severe form of dyspnea, as detailed elsewhere (7). Immediately before stent placement, three patients were classified with grade V dyspnea, six with grade IV, and five with grade III. Stent Placement and Removal The supporting stent structure was woven from a single thread of nitinol wire 0.2 mm in diameter in a tubular configuration and was bonded to the external surface of the PTFE membrane (AG Fluoropolymers, Wilmington, DE) with use of a polyurethane solution to prevent tissue growth through the stent wires (Taewoong, Seoul, Korea). A stent at least 10 mm longer than the stricture was selected for placement so the proximal and distal parts would rest on the upper and lower margins of the stricture, respectively. To enable stent removal, a nylon loop 2 mm in diameter was hooked inside each bend of the upper end of the stent, and another two nylon threads were passed through each
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Indications for Stent Removal (time, d)
Removed Stents
Symptom Recurrence
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survival period from the time of stent placement. The SPSS version 12.0 statistical package (SPSS, Chicago, IL) was used for analysis. A P value less than .05 was considered to indicate a significant difference. Removed stents were examined to evaluate membrane degradation or separation from wire meshes. Membrane degradation was defined as a membrane tear or opening in the PTFE covering, whereas membrane separation was defined as separation of the PTFE covering from the wire mesh associated with hyperplastic tissue ingrowth.
Elective (180) Elective (180) Stent migration (20)
Intact Membrane separation Intact
No No Yes
Stent migration (1)
Intact
Yes
Tissue hyperplasia Tissue hyperplasia (150) Elective (180) NA
Tissue hyperplasia (48) Membrane separation Intact NA
Intact Yes Yes No
NA
NA
No
RESULTS
Sputum retention (120)
Intact
No
Elective (100)
Intact
No
NA Stent migration (2)
NA Intact
No No
Sputum retention (30) NA NA
Intact NA NA
No No
NA
NA
No
The results are summarized in the Table. A total of 17 stents were successfully placed in 15 patients. In adults, stents 16 mm or 20 mm in diameter were used for the trachea, and stents 10 mm or 12 mm in diameter were used for the bronchus. A stent 10 mm in diameter was used in the trachea of the child. No serious immediate procedural complications occurred; one stent was improperly located during placement in one patient but was immediately relocated successfully with use of a retrieval hook wire. A total of 10 complications occurred after stent placement in eight patients: sputum retention (n ⫽ 4; 23.5%), migration of one bronchial and two tracheal stents (n ⫽ 3; 17.6%), and tissue hyperplasia (n ⫽ 3; 17.6%). Seven stents were removed to overcome seven complications (sputum retention, n ⫽ 2; stent migration, n ⫽ 3; and tissue hyperplasia, n ⫽ 2) in five patients. In the two patients with tracheal stent migration, the stent was removed and a second tracheal stent was inserted. Four stents were removed electively. Three bronchial stents were removed 6 months after placement in three patients (patients 1, 2, and 6) with tuberculous (n ⫽ 2) or traumatic (n ⫽ 1) stricture (Fig 2). One tracheal stent was removed 100 days after placement in one patient with non– small-cell lung cancer (patient 10) (Fig 3), and follow-up CT images showed that this patient had a marked decrease in mediastinal lymphadenopathy encasing the trachea. Of the total 11 stents removed dur-
of these nylon loops to form a larger loop (ie, drawstring) to fill the inside circumference of the proximal end of the stent (Fig 1). The end of the retrieval hook wire was shaped like a question mark to hook the stent drawstring, as previously described (1,4,9). The stent introducer set and stent retrieval set were similar to those described in previous reports (1,4,7). To assist in the determination of stent diameter and length, the severity and length of strictures were evaluated with conventional radiography/fluoroscopy, CT including three-dimensional reconstructions, and bronchoscopy. The details of stent placement and removal techniques are provided elsewhere (1,4,7). The indications for stent removal included elective removal when the stent was no longer necessary or stentrelated complications such as stent migration or marked tissue hyperplasia above and/or below the stent. In patients with benign strictures, stents were electively removed 6 months after placement (1,4). There were three types of removal technique (standard,
proximal mesh, and eversion), as detailed elsewhere (9,15). Follow-up and Analysis All patients underwent clinical and fluoroscopic examinations at 1–3 days, 1 month, and then every 3 or 6 months after placement to verify stent location and patency. In cases of stent removal, clinical and fluoroscopic examinations were performed immediately after removal, 1 month after removal, and then every 3 or 6 months. During the follow-up period, the following information was obtained: complications and related repeat interventions, improvement in respiratory status, symptom recurrence, and longterm prognosis. Among complications, sputum retention was considered when it was symptomatic and increased after stent placement. Improvement in respiratory status was defined as an improvement of more than one grade on the Hugh-Jones classification scale 1 month after stent placement. The Kaplan-Meier method was used to determine the cumulative
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3– 6) showed symptom recurrence after stent removal and underwent additional balloon dilation (n ⫽ 3) or curative surgery (n ⫽ 1). During follow-up (mean, 270.3 d; range, 30 –550 d), six patients with malignant strictures died 30 –330 days after stent placement as a result of disease progression (n ⫽ 4) or pneumonia (n ⫽ 2). The mean survival period (⫾ SD) was 362.9 ⫾ 58.6 days. Analysis of the 11 removed stents showed no cases of membrane degradation. Two stents showed membrane separation from the wire mesh associated with tissue hyperplasia originating from the airway wall. This intervening tissue hyperplasia was minimal in one patient (patient 5), whereas the area of the displaced covering material was approximately one third of the stent diameter in the other patient (patient 2). Despite these problems, the two stents were uneventfully removed with use of standard technique with antecedent balloon dilation.
DISCUSSION
Figure 1. Tracheal and bronchial PTFE-covered retrievable expandable nitinol stents. The tracheal stent (a) is flared distally, whereas the bronchial stent (b) is flared proximally and distally. The covering material is PTFE membrane. (c) Two drawstrings (arrow) and multiple nylon loops are attached to the proximal inner portion of the bronchial stent.
ing follow-up, all were removed with use of standard technique (ie, withdrawal of the stent with the hook wire grasping the drawstrings), and no difficulties were encountered. Balloon dilation before removal was necessary in two patients (patients 2 and 5), in whom hyperplasia resulted in the presence of tissue between the PTFE
covering and the stent mesh as well as at the distal portion of the stent. An improvement of greater than one Hugh-Jones classification grade was observed in 13 patients (93%) 1 month after stent placement, with one case classified in grade IV, five in grade III, six in grade II, and two in grade I. Four patients (27%; patients
Use of uncovered expandable metallic stents is limited in the airway not only because uncovered stents are not suitable for treatment of esophagorespiratory fistulas but also because tissue hyperplasia or tumor ingrowth through the wire mesh tends to repeatedly narrow the airway and make stent removal difficult (1,7,8). To overcome these shortcomings, several investigators have used covered expandable metallic stents or have created covered retrievable expandable metallic stents (1–7). The advantages of covered stents are lost if the covering materials are degraded or disrupted in situ. Polyurethane is one of the most common covering membrane materials for nonvascular luminal organ stents because it can be prepared in solution and easily forms a membrane (1,2,4,5,9 –14). However, polyurethane membrane degradation has been reported in several clinical studies of covered stent placement and removal in the airway as well as in the biliary tract and upper gastrointestinal tract (4,9,11,14). In addition, experimental phantom flow studies showed that exposure to bile resulted in polyurethane membrane biodegradation, possibly
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Figure 2. Images from a 36-year-old man with left main bronchial obstruction caused by endobronchial tuberculosis. Chest radiograph (a) and three-dimensional CT image (b) immediately before stent placement show total left lung collapse and total occlusion of the left main bronchus (arrow). He underwent placement of a left bronchial stent, which was removed after 6 months (not shown). (c) Removed stent shows separation of the PTFE membrane (arrows) from the wire mesh with intervening hyperplastic tissue (arrowhead). Chest radiograph (d) and three-dimensional CT image (e) 1 year after stent removal show a well-expanded left lung and good patency of the left main bronchus (arrow).
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Figure 3. Images from a 68-year-old man with tracheal narrowing caused by non–small-cell lung cancer with an extensive mediastinal mass. Axial CT image (a) and tracheography (b) immediately before stent placement show marked narrowing (arrow) of the midportion of the trachea caused by the mediastinal mass. (c) Stent placement performed under fluoroscopic guidance. (d) Follow-up axial CT image 75 days after stent placement shows a decrease in the mediastinal mass size and good stent expansion (arrow). (e) Stent was removed electively with use of a retrieval hook wire (arrow) 100 days after placement. Removal was uneventful and easy. (f) Removed stent shows an intact PTFE membrane.
because of the alkaline characteristics and emulsifying or detergent action of bile salts (16). Development of a non-
degradable covering material is critical because such degradation results in hyperplastic tissue or tumor tissue
ingrowth and makes stent removal difficult or even impossible. PTFE is a biocompatible and
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strongly chemical-resistant material. It has been used as a covering material in biliary, esophageal, gastroduodenal, and vascular stents (17–19), and we are unaware of any reports of membrane degradation or disruption in clinical studies of such stents. In the present study of PTFE-covered retrievable expandable nitinol stents in the airway, we found that the PTFE membrane itself was intact in all 11 removed stents. Therefore, in all cases, stent removal proceeded without difficulty with use of standard techniques, although antecedent balloon dilation was necessary in two cases. These data stand in contrast to those of Kim et al (9), who found that removal of three of 45 polyurethane-covered retrievable expandable nitinol stents was complicated as a result of tissue hyperplasia and membrane disruption. In addition, whereas the present study found that all stents could be removed with use of standard techniques, the study by Kim et al (9) found that only 37 of 45 airway stents (82%) could be removed with use of standard techniques with or without antecedent balloon dilation. Separation of the PTFE membrane from the wire mesh was observed in two stents in the present study. Because the PTFE membrane was located inside the stent wires and was attached to the stent with a polyurethane solution, membrane detachment from the stent wires might have occurred as a result of the polyurethane becoming weak or dissolving. Although removal of these two stents was not difficult, substantial tissue hyperplasia in the breach between the membrane and wire mesh would have made removal difficult. Therefore, tight attachment of the membrane to the stent mesh or placement of the membrane outside the stent should be considered. The present study found that the overall incidence of complications after PTFE-covered stent placement was similar to that reported for polyurethane-covered stent placement. The sputum retention rate in the present study (23.5%) was similar to that reported in other studies of polyurethane-covered expandable metallic
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stents (20%–38%) (2,7). Similarly, the stent migration rate (17.6%) and the incidence of tissue hyperplasia (17.6%) in the present study were similar to those reported in studies of polyurethane-covered expandable metallic stents (8.3%–17% and 16.7%, respectively) (1,2,4,7). The present study was limited by the small number of patients, limited follow-up period, and retrospective review without randomization. Therefore, no comparison was made between this study and the study of polyurethane-covered stent placement. In conclusion, PTFE-covered retrievable expandable nitinol stents were effective in the treatment of tracheobronchial strictures. Stent removal was easy with use of standard techniques, and none of the removed stents showed evidence of membrane degradation. References 1. Song HY, Shim TS, Kang SG, et al. Tracheobronchial strictures: treatment with a polyurethane-covered retrievable expandable nitinol stent—initial experience. Radiology 1999; 213:905–912. 2. Monnier P, Mudry A, Stanzel F, et al. The use of the covered Wallstent for the palliative treatment of inoperable tracheobronchial cancers: a prospective, multicenter study. Chest 1996; 110:1161–1168. 3. Madden BP, Datta S, Charokopos N. Experience with Ultraflex expandable metallic stents in the management of endobronchial pathology. Ann Thorac Surg 2002; 73:938–944. 4. Kim JH, Shin JH, Shim TS, et al. Results of temporary placement of covered retrievable expandable nitinol stents for tuberculous bronchial strictures. J Vasc Interv Radiol 2004; 15: 1003–1008. 5. Noppen M, Stratakos G, D’Haese J, et al. Removal of covered self-expandable metallic airway stents in benign disorders: indications, technique, and outcomes. Chest 2005; 127:482–487. 6. Madden BP, Park JE, Sheth A. Medium-term follow-up after deployment of Ultraflex expandable metallic stents to manage endobronchial pathology. Ann Thorac Surg 2004; 78:1898–1902. 7. Shin JH, Kim SW, Shim TS, et al. Malignant tracheobronchial strictures: palliation with covered retrievable expandable nitinol stent. J Vasc Interv Radiol 2003; 14:1525–1234.
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8. Shin JH, Song HY, Shim TS. Management of tracheobronchial strictures. Cardiovasc Intervent Radiol 2004; 27: 314–324. 9. Kim JH, Shin JH, Shim TS, et al. Efficacy and safety of a retrieval hook for removal of retrievable expandable tracheobronchial stents. J Vasc Interv Radiol 2004; 15:697–705. 10. Isayama H, Komatsu Y, Tsujino T, et al. A prospective randomised study of “covered” versus “uncovered” diamond stents for the management of distal malignant biliary obstruction. Gut 2004; 53:729–734. 11. Rossi P, Bezzi M, Salvatori FM, et al. Clinical experience with covered Wallstents for biliary malignancies: 23month follow-up. Cardiovasc Intervent Radiol 1997; 20:441–447. 12. Song HY, Lee DH, Seo TS, et al. Retrievable covered nitinol stents: experiences in 108 patients with malignant esophageal strictures. J Vasc Interv Radiol 2002; 13:285–293. 13. Song HY, Park H, Suh TS, et al. Recurrent traumatic urethral strictures near the external sphincter: treatment with a covered, retrievable, expandable nitinol stent—initial results. Radiology 2003; 226:433–440. 14. Jung GS, Song HY, Seo TS, et al. Malignant gastric outlet obstructions: treatment by means of coaxial placement of uncovered and covered expandable nitinol stents. J Vasc Interv Radiol 2002; 13:275–283. 15. Yoon CJ, Shin JH, Song HY, et al. Removal of retrievable esophageal and gastrointestinal stents: experience in 113 patients. AJR 2004; 183:1437–1444. 16. Kim DH, Kang SG, Choi JR, et al. Evaluation of the biodurability of polyurethane-covered stent using a flow phantom. Korean J Radiol 2001; 2:75– 79. 17. Petersen B, Uchida BT, Timmermans H, et al. Intravascular US-guided direct intrahepatic portacaval shunt with a PTFE-covered stent-graft: feasibility study in swine and initial clinical results. J Vasc Interv Radiol 2001; 12:475– 486. 18. Bae JI, Shin JH, Song HY, et al. Treatment of a benign anastomotic duodenojejunal stricture with a polytetrafluoroethylene-covered retrievable expandable nitinol stent. J Vasc Interv Radiol 2004; 15:769–772. 19. Bezzi M, Zolovkins A, Cantisani V, et al. New ePTFE/FEP-covered stent in the palliative treatment of malignant biliary obstruction. J Vasc Interv Radiol 2002; 13:581–589.
PURPOSE: To evaluate the clinical effectiveness of polytetrafluoroethylene (PTFE)– covered retrievable expandable nitinol stents in tracheobronchial strictures. MATERIALS AND METHODS: With fluoroscopic guidance, PTFE-covered retrievable expandable nitinol stents were placed in 15 symptomatic patients with benign (n ⴝ 6) or malignant (n ⴝ 9) tracheobronchial strictures. Complications and improvement in respiratory status were evaluated. Stents were removed electively 6 months after placement in benign strictures or if complications occurred. Membrane degradation or separation from the wire mesh was evaluated in removed stents. RESULTS: A total of 17 stents were successfully placed and were well tolerated in all patients. Sputum retention, stent migration, and tissue hyperplasia occurred in 23.5% (n ⴝ 4), 17.6% (n ⴝ 3), and 17.6% (n ⴝ 3) of stents, respectively. A total of 11 stents were successfully removed electively 6 months after placement (n ⴝ 4) or when complications occurred (n ⴝ 7). All 11 such stents were removed without difficulty with use of standard techniques, antecedent balloon dilation being necessary in two cases as a result of tissue hyperplasia. No removed stent showed signs of membrane degradation, and two removed stents showed signs of membrane separation from the mesh. CONCLUSIONS: PTFE-covered retrievable expandable nitinol stents were effective in the treatment of tracheobronchial strictures. Stent removal was easy with use of standard techniques, and no removed stent showed evidence of membrane degradation. J Vasc Interv Radiol 2006; 17:657– 663 Abbreviation:
PTFE ⫽ polytetrafluoroethylene
LARGE airway obstruction from benign or malignant causes is associated with high morbidity rates and possible early death. Recently, several investigators (1–7) have used covered expandable metallic stents as a relatively new method for the treatment of airway obstructions. Covered stents are From the Department of Radiology and the Research Institute of Radiology (J.H.S., H.Y.S., G.Y.K., Y.K.C., H.K.K., Y.J.K., H.K.Y., K.B.S.) and Department of Internal Medicine (T.S.S., S.W.K.), University of Ulsan College of Medicine, Asan Medical Center, 388-1, Pungnap-2dong, Songpa-gu, Seoul, 138-736, Korea. Received September 12, 2005; accepted December 25. Address correspondence to H.Y.S.; Email: [email protected] None of the authors have identified a conflict of interest. © SIR, 2006 DOI: 10.1097/01.RVI.0000203803.98007.9F
associated with relatively little hyperplastic tissue ingrowth and can be removed electively or in cases of complications unless the membrane is disrupted (1,4,5,8,9). Several recent reports (4,5,9) have specifically highlighted the importance of covered stent removal in patients with benign airway strictures. Polyurethane has been widely used to cover expandable metallic stents for the airway and esophagus, gastrointestinal tract, biliary tract, and urethra (1,2,4,5,9 –14). However, polyurethane degradation has been reported when such stents were inserted in the airway, biliary tract, and upper gastrointestinal tract for long periods of time (4,9,11,14). Those reports suggested that respiratory secretions or gastric juices are capable of damaging or perforating polyurethane membranes,
and they found that removal of stents with damaged membranes was difficult as a result of hyperplastic tissue ingrowth through perforations. To overcome shortcomings associated with polyurethane-covered stents, we designed retrievable expandable metallic stents covered with polytetrafluoroethylene (PTFE), which is a strong chemical-resistant material. The present study evaluated the clinical effectiveness of PTFE-covered retrievable expandable nitinol stents in patients with tracheobronchial strictures.
MATERIALS AND METHODS Patients From October 2003 to March 2005, 15 consecutive patients (10 male and five female; age range, 2– 68 years;
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PTFE-Covered Retrievable Expandable Nitinol Stent Placement in 15 Patients Stent Size Patient Age No. (y) Sex
Cause
Location of Strictures
Hugh-Jones Grade
Diameter Length (mm) (cm)
Before
After
Complications
1 2 3
25 36 38
M M F
Traumatic Tuberculous Tuberculous
Left main bronchus Left main bronchus Left main bronchus
12 12 10
4 3 4
III III III
I I II
4
53
F
After intubation
Trachea
16
5
V
III
5 6 7
36 22 2
F F F
Left main bronchus Left main bronchus Trachea
16 12 12 10
6 5 4 3
III II IV III Ventilated state
8
64
M
4
III
II
None
54
M
Left main and lowerlimb bronchus Left main bronchus
12
9
12
4
IV
IV
Sputum retention
10
68
M
Trachea
20
5
IV
II
Sputum retention
11 12
54 62
M M
Tuberculous Tuberculous Mediastinal primitive embryonal sarcoma Non–small-cell lung cancer Non–small-cell lung cancer Non–small-cell lung cancer Esophageal cancer Non–small-cell lung cancer
None Tissue hyperplasia Stent migration (proximal) Stent migration (proximal) Tissue hyperplasia Tissue hyperplasia None None
Trachea Trachea
20 20
6 6
IV V
III III
13 14
33 50
M M
9 9 5
V IV
III II
62
M
Trachea Left main and lowerlobe bronchus Trachea
20 20 12
15
Esophageal cancer Non–small-cell lung cancer Esophageal cancer
Sputum retention Stent migration (distal) Sputum retention None None
20
8
IV
II
None
mean age, 44 y) with tracheobronchial obstructions underwent fluoroscopically guided placement of PTFE-covered retrievable expandable nitinol stents. Our institution does not require institutional review board approval for retrospective reviews of patient records or images. The causes of the tracheobronchial obstructions were benign in six patients (tuberculous stricture, n ⫽ 4; traumatic bronchial stricture, n ⫽ 1; stenosis after intubation, n ⫽ 1) and malignant in nine patients (non–small cell-lung cancer, n ⫽ 5; esophageal cancer, n ⫽ 3; mediastinal primitive embryonal sarcoma, n ⫽ 1) (Table). The diagnosis of traumatic bronchial stricture and stenosis after intubation was made by bronchoscopy and computed tomography (CT) on the basis of relevant clinical histories. The diagnosis of other diseases was established by bronchoscopic or percutaneous biopsy. The obstruction sites were at the trachea (n ⫽ 7), left main bronchus (n ⫽ 6), and left main/lower bronchus (n ⫽ 2). Three patients with esophageal cancer reported dyspnea resulting
from tracheal invasion secondary to esophageal cancer, and one such patient (patient 13) already had an esophageal stent that had been placed 3 months previously. In five of the six patients with benign obstruction, the PTFE-covered stents were used as a result of failure of previous balloon dilation (n ⫽ 5) and/or polyurethane-covered stent placement (n ⫽ 4), whereas PTFE-covered stents were used in the primary treatment of the nine malignant obstructions and one near-complete benign obstruction (patient 2). One child with mediastinal primitive embryonal sarcoma (patient 7) was in a mechanically ventilated state, whereas the remaining 14 patients, all of whom were adults, had resting or exertional dyspnea. The Hugh-Jones classification was used to evaluate improvement in respiratory function before and 1 month after stent placement in the 14 adult patients but not in the child, who required ventilation. This classification is a five-grade system used to assess breathlessness on the basis of daily ac-
tivities, with grade V indicating the most severe form of dyspnea, as detailed elsewhere (7). Immediately before stent placement, three patients were classified with grade V dyspnea, six with grade IV, and five with grade III. Stent Placement and Removal The supporting stent structure was woven from a single thread of nitinol wire 0.2 mm in diameter in a tubular configuration and was bonded to the external surface of the PTFE membrane (AG Fluoropolymers, Wilmington, DE) with use of a polyurethane solution to prevent tissue growth through the stent wires (Taewoong, Seoul, Korea). A stent at least 10 mm longer than the stricture was selected for placement so the proximal and distal parts would rest on the upper and lower margins of the stricture, respectively. To enable stent removal, a nylon loop 2 mm in diameter was hooked inside each bend of the upper end of the stent, and another two nylon threads were passed through each
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Indications for Stent Removal (time, d)
Removed Stents
Symptom Recurrence
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survival period from the time of stent placement. The SPSS version 12.0 statistical package (SPSS, Chicago, IL) was used for analysis. A P value less than .05 was considered to indicate a significant difference. Removed stents were examined to evaluate membrane degradation or separation from wire meshes. Membrane degradation was defined as a membrane tear or opening in the PTFE covering, whereas membrane separation was defined as separation of the PTFE covering from the wire mesh associated with hyperplastic tissue ingrowth.
Elective (180) Elective (180) Stent migration (20)
Intact Membrane separation Intact
No No Yes
Stent migration (1)
Intact
Yes
Tissue hyperplasia Tissue hyperplasia (150) Elective (180) NA
Tissue hyperplasia (48) Membrane separation Intact NA
Intact Yes Yes No
NA
NA
No
RESULTS
Sputum retention (120)
Intact
No
Elective (100)
Intact
No
NA Stent migration (2)
NA Intact
No No
Sputum retention (30) NA NA
Intact NA NA
No No
NA
NA
No
The results are summarized in the Table. A total of 17 stents were successfully placed in 15 patients. In adults, stents 16 mm or 20 mm in diameter were used for the trachea, and stents 10 mm or 12 mm in diameter were used for the bronchus. A stent 10 mm in diameter was used in the trachea of the child. No serious immediate procedural complications occurred; one stent was improperly located during placement in one patient but was immediately relocated successfully with use of a retrieval hook wire. A total of 10 complications occurred after stent placement in eight patients: sputum retention (n ⫽ 4; 23.5%), migration of one bronchial and two tracheal stents (n ⫽ 3; 17.6%), and tissue hyperplasia (n ⫽ 3; 17.6%). Seven stents were removed to overcome seven complications (sputum retention, n ⫽ 2; stent migration, n ⫽ 3; and tissue hyperplasia, n ⫽ 2) in five patients. In the two patients with tracheal stent migration, the stent was removed and a second tracheal stent was inserted. Four stents were removed electively. Three bronchial stents were removed 6 months after placement in three patients (patients 1, 2, and 6) with tuberculous (n ⫽ 2) or traumatic (n ⫽ 1) stricture (Fig 2). One tracheal stent was removed 100 days after placement in one patient with non– small-cell lung cancer (patient 10) (Fig 3), and follow-up CT images showed that this patient had a marked decrease in mediastinal lymphadenopathy encasing the trachea. Of the total 11 stents removed dur-
of these nylon loops to form a larger loop (ie, drawstring) to fill the inside circumference of the proximal end of the stent (Fig 1). The end of the retrieval hook wire was shaped like a question mark to hook the stent drawstring, as previously described (1,4,9). The stent introducer set and stent retrieval set were similar to those described in previous reports (1,4,7). To assist in the determination of stent diameter and length, the severity and length of strictures were evaluated with conventional radiography/fluoroscopy, CT including three-dimensional reconstructions, and bronchoscopy. The details of stent placement and removal techniques are provided elsewhere (1,4,7). The indications for stent removal included elective removal when the stent was no longer necessary or stentrelated complications such as stent migration or marked tissue hyperplasia above and/or below the stent. In patients with benign strictures, stents were electively removed 6 months after placement (1,4). There were three types of removal technique (standard,
proximal mesh, and eversion), as detailed elsewhere (9,15). Follow-up and Analysis All patients underwent clinical and fluoroscopic examinations at 1–3 days, 1 month, and then every 3 or 6 months after placement to verify stent location and patency. In cases of stent removal, clinical and fluoroscopic examinations were performed immediately after removal, 1 month after removal, and then every 3 or 6 months. During the follow-up period, the following information was obtained: complications and related repeat interventions, improvement in respiratory status, symptom recurrence, and longterm prognosis. Among complications, sputum retention was considered when it was symptomatic and increased after stent placement. Improvement in respiratory status was defined as an improvement of more than one grade on the Hugh-Jones classification scale 1 month after stent placement. The Kaplan-Meier method was used to determine the cumulative
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3– 6) showed symptom recurrence after stent removal and underwent additional balloon dilation (n ⫽ 3) or curative surgery (n ⫽ 1). During follow-up (mean, 270.3 d; range, 30 –550 d), six patients with malignant strictures died 30 –330 days after stent placement as a result of disease progression (n ⫽ 4) or pneumonia (n ⫽ 2). The mean survival period (⫾ SD) was 362.9 ⫾ 58.6 days. Analysis of the 11 removed stents showed no cases of membrane degradation. Two stents showed membrane separation from the wire mesh associated with tissue hyperplasia originating from the airway wall. This intervening tissue hyperplasia was minimal in one patient (patient 5), whereas the area of the displaced covering material was approximately one third of the stent diameter in the other patient (patient 2). Despite these problems, the two stents were uneventfully removed with use of standard technique with antecedent balloon dilation.
DISCUSSION
Figure 1. Tracheal and bronchial PTFE-covered retrievable expandable nitinol stents. The tracheal stent (a) is flared distally, whereas the bronchial stent (b) is flared proximally and distally. The covering material is PTFE membrane. (c) Two drawstrings (arrow) and multiple nylon loops are attached to the proximal inner portion of the bronchial stent.
ing follow-up, all were removed with use of standard technique (ie, withdrawal of the stent with the hook wire grasping the drawstrings), and no difficulties were encountered. Balloon dilation before removal was necessary in two patients (patients 2 and 5), in whom hyperplasia resulted in the presence of tissue between the PTFE
covering and the stent mesh as well as at the distal portion of the stent. An improvement of greater than one Hugh-Jones classification grade was observed in 13 patients (93%) 1 month after stent placement, with one case classified in grade IV, five in grade III, six in grade II, and two in grade I. Four patients (27%; patients
Use of uncovered expandable metallic stents is limited in the airway not only because uncovered stents are not suitable for treatment of esophagorespiratory fistulas but also because tissue hyperplasia or tumor ingrowth through the wire mesh tends to repeatedly narrow the airway and make stent removal difficult (1,7,8). To overcome these shortcomings, several investigators have used covered expandable metallic stents or have created covered retrievable expandable metallic stents (1–7). The advantages of covered stents are lost if the covering materials are degraded or disrupted in situ. Polyurethane is one of the most common covering membrane materials for nonvascular luminal organ stents because it can be prepared in solution and easily forms a membrane (1,2,4,5,9 –14). However, polyurethane membrane degradation has been reported in several clinical studies of covered stent placement and removal in the airway as well as in the biliary tract and upper gastrointestinal tract (4,9,11,14). In addition, experimental phantom flow studies showed that exposure to bile resulted in polyurethane membrane biodegradation, possibly
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Figure 2. Images from a 36-year-old man with left main bronchial obstruction caused by endobronchial tuberculosis. Chest radiograph (a) and three-dimensional CT image (b) immediately before stent placement show total left lung collapse and total occlusion of the left main bronchus (arrow). He underwent placement of a left bronchial stent, which was removed after 6 months (not shown). (c) Removed stent shows separation of the PTFE membrane (arrows) from the wire mesh with intervening hyperplastic tissue (arrowhead). Chest radiograph (d) and three-dimensional CT image (e) 1 year after stent removal show a well-expanded left lung and good patency of the left main bronchus (arrow).
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Figure 3. Images from a 68-year-old man with tracheal narrowing caused by non–small-cell lung cancer with an extensive mediastinal mass. Axial CT image (a) and tracheography (b) immediately before stent placement show marked narrowing (arrow) of the midportion of the trachea caused by the mediastinal mass. (c) Stent placement performed under fluoroscopic guidance. (d) Follow-up axial CT image 75 days after stent placement shows a decrease in the mediastinal mass size and good stent expansion (arrow). (e) Stent was removed electively with use of a retrieval hook wire (arrow) 100 days after placement. Removal was uneventful and easy. (f) Removed stent shows an intact PTFE membrane.
because of the alkaline characteristics and emulsifying or detergent action of bile salts (16). Development of a non-
degradable covering material is critical because such degradation results in hyperplastic tissue or tumor tissue
ingrowth and makes stent removal difficult or even impossible. PTFE is a biocompatible and
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strongly chemical-resistant material. It has been used as a covering material in biliary, esophageal, gastroduodenal, and vascular stents (17–19), and we are unaware of any reports of membrane degradation or disruption in clinical studies of such stents. In the present study of PTFE-covered retrievable expandable nitinol stents in the airway, we found that the PTFE membrane itself was intact in all 11 removed stents. Therefore, in all cases, stent removal proceeded without difficulty with use of standard techniques, although antecedent balloon dilation was necessary in two cases. These data stand in contrast to those of Kim et al (9), who found that removal of three of 45 polyurethane-covered retrievable expandable nitinol stents was complicated as a result of tissue hyperplasia and membrane disruption. In addition, whereas the present study found that all stents could be removed with use of standard techniques, the study by Kim et al (9) found that only 37 of 45 airway stents (82%) could be removed with use of standard techniques with or without antecedent balloon dilation. Separation of the PTFE membrane from the wire mesh was observed in two stents in the present study. Because the PTFE membrane was located inside the stent wires and was attached to the stent with a polyurethane solution, membrane detachment from the stent wires might have occurred as a result of the polyurethane becoming weak or dissolving. Although removal of these two stents was not difficult, substantial tissue hyperplasia in the breach between the membrane and wire mesh would have made removal difficult. Therefore, tight attachment of the membrane to the stent mesh or placement of the membrane outside the stent should be considered. The present study found that the overall incidence of complications after PTFE-covered stent placement was similar to that reported for polyurethane-covered stent placement. The sputum retention rate in the present study (23.5%) was similar to that reported in other studies of polyurethane-covered expandable metallic
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stents (20%–38%) (2,7). Similarly, the stent migration rate (17.6%) and the incidence of tissue hyperplasia (17.6%) in the present study were similar to those reported in studies of polyurethane-covered expandable metallic stents (8.3%–17% and 16.7%, respectively) (1,2,4,7). The present study was limited by the small number of patients, limited follow-up period, and retrospective review without randomization. Therefore, no comparison was made between this study and the study of polyurethane-covered stent placement. In conclusion, PTFE-covered retrievable expandable nitinol stents were effective in the treatment of tracheobronchial strictures. Stent removal was easy with use of standard techniques, and none of the removed stents showed evidence of membrane degradation. References 1. Song HY, Shim TS, Kang SG, et al. Tracheobronchial strictures: treatment with a polyurethane-covered retrievable expandable nitinol stent—initial experience. Radiology 1999; 213:905–912. 2. Monnier P, Mudry A, Stanzel F, et al. The use of the covered Wallstent for the palliative treatment of inoperable tracheobronchial cancers: a prospective, multicenter study. Chest 1996; 110:1161–1168. 3. Madden BP, Datta S, Charokopos N. Experience with Ultraflex expandable metallic stents in the management of endobronchial pathology. Ann Thorac Surg 2002; 73:938–944. 4. Kim JH, Shin JH, Shim TS, et al. Results of temporary placement of covered retrievable expandable nitinol stents for tuberculous bronchial strictures. J Vasc Interv Radiol 2004; 15: 1003–1008. 5. Noppen M, Stratakos G, D’Haese J, et al. Removal of covered self-expandable metallic airway stents in benign disorders: indications, technique, and outcomes. Chest 2005; 127:482–487. 6. Madden BP, Park JE, Sheth A. Medium-term follow-up after deployment of Ultraflex expandable metallic stents to manage endobronchial pathology. Ann Thorac Surg 2004; 78:1898–1902. 7. Shin JH, Kim SW, Shim TS, et al. Malignant tracheobronchial strictures: palliation with covered retrievable expandable nitinol stent. J Vasc Interv Radiol 2003; 14:1525–1234.
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8. Shin JH, Song HY, Shim TS. Management of tracheobronchial strictures. Cardiovasc Intervent Radiol 2004; 27: 314–324. 9. Kim JH, Shin JH, Shim TS, et al. Efficacy and safety of a retrieval hook for removal of retrievable expandable tracheobronchial stents. J Vasc Interv Radiol 2004; 15:697–705. 10. Isayama H, Komatsu Y, Tsujino T, et al. A prospective randomised study of “covered” versus “uncovered” diamond stents for the management of distal malignant biliary obstruction. Gut 2004; 53:729–734. 11. Rossi P, Bezzi M, Salvatori FM, et al. Clinical experience with covered Wallstents for biliary malignancies: 23month follow-up. Cardiovasc Intervent Radiol 1997; 20:441–447. 12. Song HY, Lee DH, Seo TS, et al. Retrievable covered nitinol stents: experiences in 108 patients with malignant esophageal strictures. J Vasc Interv Radiol 2002; 13:285–293. 13. Song HY, Park H, Suh TS, et al. Recurrent traumatic urethral strictures near the external sphincter: treatment with a covered, retrievable, expandable nitinol stent—initial results. Radiology 2003; 226:433–440. 14. Jung GS, Song HY, Seo TS, et al. Malignant gastric outlet obstructions: treatment by means of coaxial placement of uncovered and covered expandable nitinol stents. J Vasc Interv Radiol 2002; 13:275–283. 15. Yoon CJ, Shin JH, Song HY, et al. Removal of retrievable esophageal and gastrointestinal stents: experience in 113 patients. AJR 2004; 183:1437–1444. 16. Kim DH, Kang SG, Choi JR, et al. Evaluation of the biodurability of polyurethane-covered stent using a flow phantom. Korean J Radiol 2001; 2:75– 79. 17. Petersen B, Uchida BT, Timmermans H, et al. Intravascular US-guided direct intrahepatic portacaval shunt with a PTFE-covered stent-graft: feasibility study in swine and initial clinical results. J Vasc Interv Radiol 2001; 12:475– 486. 18. Bae JI, Shin JH, Song HY, et al. Treatment of a benign anastomotic duodenojejunal stricture with a polytetrafluoroethylene-covered retrievable expandable nitinol stent. J Vasc Interv Radiol 2004; 15:769–772. 19. Bezzi M, Zolovkins A, Cantisani V, et al. New ePTFE/FEP-covered stent in the palliative treatment of malignant biliary obstruction. J Vasc Interv Radiol 2002; 13:581–589.