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a Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
b Department of Thoracic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
Accepted for publication April 22, 2009.
* Address correspondence to Dr Hojoong Kim, Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul, 135-710, Republic of Korea (Email: hjk3425{at}skku.edu).
| Dr Hojoong Kim discloses a financial relationship with TNO and E1S Company.
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Abstract |
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Methods: Between January 2004 and February 2008, 11 patients underwent ballooning, neodymium:yttrium-aluminum-garnet laser resection, or bougienation (by rigid bronchoscopy) to dilate the airway, followed by placement of the Natural Y stent.
Results: The underlying etiologies of carinal stenosis included posttuberculosis stricture in 7 patients (64%), postintubation stenosis in 2 (18%), and postoperative malacia in 2 (18%). All patients reported subjective symptomatic relief immediately after stent placement. No procedurally related deaths or immediate major complications occurred. Stent-related late complications included granulation tissue formation (64%) and mucostasis (18%, defined as 
50% narrowing). The median duration of overall stent placement was 439 days (range, 119 to 1729 days). The stents were successfully removed in 4 patients (36%) after a median of 409 days.
Conclusions: The Natural Y stent provides an effective and feasible therapeutic modality in patients with benign carinal stenosis, with or without previous thoracic airway interventions.
Benign airway stenosis in adult patients may arise as a complication of intubation, tracheostomy, airway trauma, tracheobronchomalacia, or anastomosis, such as in lung transplantation [1–3]. Airway stenosis may also occur as a result of medical conditions such as tuberculosis, relapsing polychondritis, or congenital conditions [4–6].
Depending on the site of the lesion and the severity of the narrowing, stenosis may cause dyspnea, respiratory distress, or obstructive pneumonia; such patients are frequently within hours or days of death due to suffocation. Several surgical and bronchoscopic approaches are available for the management of airway stenosis, including surgical resection, laser therapy, balloon dilatation, and stent placement [7–10].
When the obstruction is located in the carinal region, the use of straight stents is limited due to the Y-shaped anatomy of the carina. Therefore, Y-shaped stents are necessary to treat airway obstructions involving the carinal region. The most commonly used Y-stent in the carinal region is the silicone Dumon stent [11, 12], followed by the dynamic stent developed by Freitag and coworkers [13] and the Y-shaped metallic stent [14]. However, scanty information is available regarding the efficacy of Y-shaped airway stents in benign airway stenosis involving the carinal region.
In 2002, we designed a modified dynamic and Dumon silicone stent named the Natural stent (Fig 1A). Previous studies in a canine model of tracheal stenosis and in patients with benign tracheobronchial stenosis showed that the Natural stent was as effective and safe as the Dumon stent [15, 16]. The Natural Y stent is a Y-shaped silicone stent designed for the trachea and bronchus (Fig 1B). Since 2004, the Natural Y stent has been the prosthesis of choice to treat patients with airway disease at our institution. This study investigated the role and clinical efficacy of the Natural Y stent in the management of benign airway disease involving the carinal region.
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Material and Methods |
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Patients
This study included 11 patients who were referred to our hospital for the management of benign carinal stenosis. All patients underwent consecutive Natural Y stent placement. The demographic characteristics, treatment modalities, type of airway stenosis, occurrence of procedurally related complications, and clinical outcomes were assessed by retrospective medical record review. Tracheobronchial complications were determined by 3-dimensional computed tomography (3DCT) or flexible bronchoscopy, or both. In 10 patients, routine spirometry was tested before and after stent placement, and the results are expressed as predicted percentages (% predicted).
During the follow-up period, respiratory symptoms, and findings on chest roentgenogram and spirometry were monitored. Repeated flexible bronchoscopy, roentgenogram, or 3DCT was used to reassess stent position and patency. Patients were followed up monthly at our clinic or more frequently if they showed a deteriorating clinical course.
The Natural Y Stent
In 2002, we introduced a novel stent named the Natural stent, which was developed and manufactured by TNO Company, Seoul, Korea. This stent is made of molded silicone and is straight. It features a horizontal C-shaped circular threads on its outer surface by interposing a flexible posterior wall, which mimics the posterior membrane of the trachea for the trachea stenosis, or external round threads without an interposing smooth wall for bronchial stenosis (Fig 1A). The Natural Y-shaped stent evaluated in this study (Fig 1B) consists of a main tracheal stent (inner diameter, 10 to 14 mm; outer diameter, 11 to 15 mm) and bifurcated main bronchial stents (inner diameter, 8 mm; outer diameter, 9 mm) and was designed to treat airway disease involving the carinal region. An adequate size of stent was selected and used as determined by the interventional pulmonologist.
Airway Intervention
All patients underwent rigid bronchoscopy under general anesthesia induced by intravenous propofol. The patients were then intubated with a rigid Hopkins bronchoscope tube (Karl-Storz, Tuttlingen, Germany). An initial exploration of the tracheobronchial tree was sometimes followed by a more detailed examination with a flexible bronchoscope (EVIS BF 1T240, Olympus, Tokyo, Japan) through the rigid bronchoscope.
For ballooning, a 10- or 12-mm controlled radial expansion balloon (Boston Scientific, Natick, MA) was inflated two or three times to 3 atm for 20 seconds. When localized dense fibrosis was observed, a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (LaserSonics, Milpitas, CA) was used to cut the fibrotic bands using a G56D noncontact fiber (LaserSonics). Stenoses were also gently dilated mechanically using a rigid bronchoscope, followed immediately by stent insertion.
In general, the criteria for the Natural Y stent placement in benign airway disease at our institution included patients who showed:
The Natural Y stent of an appropriate size is grasped from the inside using Y stent introducer forceps (Karl-Storz, Tuttlingen, Germany; Fig 2) and inserted with its bronchial limbs folded together. Under direct laryngoscopy, the straightened Y stent is inserted past the vocal cords on the Y stent introducer forceps, deposited above the carina, and then advanced gently. Once in place, the introducer forceps are carefully opened, and the bronchial limbs can be felt extending into their respective main bronchi. With the stent in place, the introducer forceps are withdrawn, and the patient is intubated with the rigid bronchoscope to verify stent position and patency.
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Results |
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Bronchoscopic Findings and Interventions
Bronchoscopic findings and interventions are summarized in Table 1. The types of stenosis included fibrous stricture in 7 patients (64%) and malacia in 4 (36%). Before Y-stent insertion, bougienage was the most common method of airway dilatation (82%). All patients had previously undergone straight stent placement, with silicone stents in 9 and metallic stents in 2 patients. Representative patients are presented in Figures 3, 4, and 5.
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The median follow-up duration from placement of Y stent to either death or close date was 1342 days (range, 286 to 1729 days), and the median duration of stent placement for all patients was 439 days (range, 119 to 1729 days). The Y stents were removed successfully in 4 patients (36%) after a median placement of 409 days, and 3 of these patients required a straight Natural stent. The remaining 7 patients, including 1 patient who died within 286 days of stent insertion of congestive heart failure, tolerated prolonged stent placement for a median period of 973 days.
Spirometry data were collected at 3 months after the intervention. The median FEV1% predicted was 68.5% (range, 36% to 105%), FVC% predicted was 78% (range, 41% to 114%), and the FEV1/FVC ratio was 70% (range, 60% to 80%). Compared with the baseline values, the median FEV1% predicted improved significantly. The Wilcoxon signed-ranks test was used for paired continuous FEV1 data (p < 0.05 was considered significant; Fig 6).
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Comment |
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Tracheobronchial stenosis caused by benign or malignant disease frequently results in dyspnea, which may be life threatening. Airway resection and reconstruction provide the most reliable definitive correction for benign airway disease, but airway stent insertion has produced tolerable results in patients with some benign airway stenoses [2, 17–19]. The carinal bifurcation is a region in which it is generally difficult to maintain a sufficient airway because of its Y-shaped anatomic structure. A Y-shaped silicone rubber stent was first designed by Westaby and colleagues [20], but Freitag and coworkers [13] and Dumon [18] later developed Y-shaped stents that could be inserted through a bronchoscope without the need for tracheostomy. The device described here can also be introduced through a rigid bronchoscope using a specially designed instrument (Fig 2). Metallic Y-shaped stents [14] are also available for the treatment of carinal stenosis.
An ideal airway stent in general should be atraumatic with respect to the airway wall, well anchored to the wall, thin with a wide internal lumen, easily inserted and removed, available in different diameters and lengths, and inexpensive [21]. Therefore, new investigatons have been initiated to make a more physiologic, biocompatible airway stent. The dynamic stent that was developed by Freitag and coworkers [22] was based on ex vivo experiments and aerodynamic studies. They incorporated a C-shaped cross section into the stent design by interposing a flexible posterior membrain to widen the stenotic trachea and to maintain physiologic tracheal movement. However, the dynamic stent is limited by excessive rigidity of the tracheal portion and by the difficulty of stent placement [13]. Also, the external surface of Dumon stent is covered with regularly placed studs to prevent dislodgement, which may cause trauma to the airway wall.
These limitations prompted us to develop a silicone stent named the Natural stent, with the goal of treating tracheobronchial stenosis. The stent is degined to increse fixation and allow physiologic movement like the dynamic stent. This design, that features a horizontal C-shaped thread on its outer surface by interposing a flexible posterior membrane, gives the Natural stent several advantages, including increased stent-to-wall contact, maintenance of physiologic airway constriction or dilatation, increased inner diameter, and less expense. A previous study has demonstrated that the Natural stent is as effective and safe as the Dumon stent in benign thracheobronchial stenoses [5, 15, 16].
Although some progress has been made in managing single or double stenoses, we have found it difficult to manage stenosis in the carinal region. Therefore, we designed the Natural Y-shaped stent, which consists of a main tracheal Natural stent with bifurcated main bronchial stents for the treatment of patients with airway disease involving the carina. Six of the patients described in this study had undergone previous thoracic airway operations, including surgical resection and reanastomosis in 3, tracheostomy in 2, and external stent placement using a vascular graft in 1. In addition to these 6 patients, 5 required additional brochoscopic intervention despite the repeated use of straight stents. Aafter Natural Y stent placement, however, satisfactory airway patency was maintained in all patients. These results suggest that airway stents may be useful in treating airway complications after thoracic airway operations and that the Natural Y-shaped stent is a particularly effective way to manage benign carinal stenosis.
The most commonly used Y stent is the silicone Dumon stent, followed by the dynamic stent, both of which are inserted using a rigid bronchoscope under general anesthesia. This stent has been used to successfully manage patients with tracheobronchial stenosis or fistulas in the carinal region [11–13, 23]. The use of a self-expandable, inverted, Y-shaped metallic stent (mesh stent) has been reported in the management of carinal stenosis [14, 24]. Most patients in these previous studies required Y stent procedures as a result of malignant disease. A recent prospective observational study has reported that central airway stabilization with silicon Dumon stents (27 Y stent cases, 47%) can improve respiratory symptoms in patients with exclusive severe symptomatic tracheobronchomalacia before thoracic operations [2]. In our study, however, all patients had several benign airway disease, such as posttuberculosis stricture, postintubation stenosis, and postoperative malacia, with or without previous thoracic airway operations. Therefore, although this study was retrospective and had a small number of patients, it does report benign carinal stenosis, including patients with previously thoracic surgery, managed by bronchoscopic intervention using a silicone Y stent.
Previous reports of complications with straight silicone stents showed that migration, mucostasis, and the developement of granulation tissue are frequent findings [5, 16, 17, 19, 25]. Migration rates vary from 20% to 50%, and migration occurs more frequently in benign stenosis than in malignant disease. A previous study using the Dumon Y stent in malignant disease observed migration in only 1 patient (1%) during a mean stent placement period of 133 days [11]. A second study using the dynamic stent in patients with malignant (70%) and benign (30%) disease reported migration in 3% of patients, granulation tissue formation in 4%, and mucostasis in 1 (1%) during mean stent placement periods of 69 days in survivors and 123 days in nonsurvivors.
Another study using the Dumon stent (27 tent cases, 47%) in benign disease with tracheobronchomalacia reported that 90% of cases have a stent-related complication such as stent migration and impaction with mucosa plug, which make this approach less suitable for a long-term solution. Complications and duration of follow-up related to Y stent use, however, has not been reported [2]. In present study, stent-related late complications included granulation tissue formation in 7 patients (64%), who required additional procedures such as a laser resection or tissue removal using forceps, and mucostasis in 2 (18%), who required toileting therapy. Granulation tissue developed at the proximal and distal ends of the stent in 6 patients, requiring the insertion of a new, longer Y stent. The reason for the relatively high incidence of granulation or mucostasis is likely the prolonged period of stent placement (median of 439 days among all patients) due to benign airway disease. The longest duration of stent placement was 1729 days. In general, fibrotic scarring may become exaggerated during long periods of stent replacement, resulting in granuloma formation and restenosis, although stent migration was not observed. The Y stent, saddled on the carina, neatly solves the problem of migration commonly observed with straight stents.
The Y stent was successfully removed from 4 patients (36%) in our study after a median of 409 days. The remaining 7 patients required prolonged stent placement for a median of 973 days. One of the 4 patients who underwent Y stent removal required no further bronchoscopic intervention. The remaining 3 patients needed the placement of a straight stent due to recurrent airway stenosis or malacia. However, they required the smaller straight stent rather than the Y stent. Ten of the 11 patients are still living. One patient died of underlying congestive heart failure 286 days after stent insertion. The median FEV1% predicted improved significantly after Y stent placement (Fig 6), and all patients reported subjective symptomatic relief immediately after stent placement. Overall, Natural Y stents were well tolerated and effective in patients with benign carinal stenosis.
The insertion of a silicone Y stent requires the use of a rigid bronchoscope under general anesthesia and a dedicated instrument. In general, conformity to the contours of the trachea while minimizing contact with the mucosa limits granuloma formation. Therefore, stent placement should be prefaced by "gentle" predilation of the trachea using a laser, mechanical dissection, or bougienage, and not by direct dilation with the stent itself.
The removal of the silicone Y stent is simple and almost identical to the technique used for the removal of conventional straight silicone stents. In contrast to these silicone stents, metallic stents have several disadvantages, including the difficulty of removal and ingrowth of granulation tissue, leading to reocclusion of the lumen [26]. Two patients in this study were referred to our hospital because of metallic stent-related reocclusion and were subsequently treated with the Natural Y stent after removal of the metallic stent. They are currently in stable condition, without central airway obstruction.
This study has several limitations. First, it was not a comparative or prospective study; therefore, the treatment approach was decided by the bronchoscopist on a case-by-case basis. The procedures were performed consistently using accepted methods, however, and all were performed by the same bronchoscopist. Second, because benign carinal stenosis is a rare condition, the study sample was relatively small.
In conclusion, although further clinical trials are needed, our clinical results indicate that the Natural Y stent provides an efficacious and feasible therapeutic modality in patients with benign carinal stenosis, with or without previous thoracic airway interventions. Further stent development is required to reduce the late complication rate.
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