Long-term follow-up of self-expandable metallic stents in benign tracheobronchial stenosis: a retrospective study

Airway obstruction is potentially life-threatening. Corrective therapies to guarantee a sufficient airstream are essential for patients with severe tracheobronchial obstructions. There are several surgical and nonsurgical therapies available in clinic. A cutting-edge nonsurgical therapy is bronchoscopic airway stenting. Tracheal stenting for symptomatic stenosis is reserved for patients with lesions that are deemed unresectable, due to local or general conditions [1]. Treatment for benign tracheobronchial stenosis treated with stenting includes post-inflammatory stenosis (after tuberculosis or airway fungal disease), post-traumatic stenosis (after intubation or tracheostomy), post-anastomotic stenosis (after lung transplantation), and extrinsic compression [2].

The use of self-expandable metallic stents (SEMSs) has become a common procedure, mainly in malignant tracheobronchial stenosis. For benign tracheobronchial lesions, silicone stents are preferred. Previously, however, silicone stents were not available in some developing countries. Thus, some interventional pulmonologists have also used SEMSs in benign tracheal stenosis, and there is still controversy with respect to the long-term patency and complications of this therapy. Moreover, due to the lack of comprehensive observations on the efficacy and long-term outcomes this treatment remains controversial. This procedure has been performed at our institution for nearly 13 years in a variety of benign tracheal stenosis procedures, and approximately 10 years of follow-up data are now available. Thus, the purpose of this study was to retrospectively determine the efficacy and long-term outcomes in patients who have undergone tracheobronchial metal stent placement for benign diseases.

The present study shows a single institution’s experience in the management of tracheobronchial obstruction with SEMSs in benign diseases. Several reports dedicated to SEMSs have been published, but none included such a large quantity of patients or long-term follow-up [8‐20].

Post-tuberculosis tracheobronchial stenosis (PTTS) and post-traumatic stenosis (after intubation or tracheostomy) are considered to be the most common two causes of benign airway stenosis [21, 22]. Our study showed similar results in that the main causes of stricture were PTTS (47.41%) and post-traumatic stenosis (45.69%). In 55 patients with PTTS, 36 SEMSs were implanted in the left main stem bronchus, which indicated bronchial tuberculosis amenable to stenting and frequently occurred on the left side. Compared with the previous largest series [4, 9], our study included a greater quantity of patients and showed a higher rate of clinical improvement (84.48%, n = 116 versus 62.9%, n = 69, and 76.7%, n = 72 respectively). Technical success was implemented in 100% of individuals, and clinical success was achieved in 66.67% (95% CI: 57.52–75.82%). None of the deaths stated in our study were associated to stent implantation or its longevity in the airway. Madan et al. [23] reported a multicenter experience with the placement of metallic Y stents, but all patients in that study had malignant airway obstruction or airway fistulization near the tracheal carina. In our study, Y stents were inserted in one patient with relapsing polychondritis.

The Food and Drug Administration recommendation in 2005 stated that the use of metallic stents to treat benign tracheal stenosis should be considered only after thorough exploration of all other treatment options, like surgical treatment or insertion of silicone stents [24]. However, silicone stents were not available in some developing countries in previous years. Compared to silicone stents, SEMSs have their advantages, such as lower migration rate, better conformation to irregular airways, greater cross-sectional airway diameter because of thinner wall construction, in favor of mucociliary clearance due to epithelialization within the stent, and a greater ease of placement [4]. Moreover, SEMSs can be successfully placed with a flexible bronchoscope under conscious sedation and local anesthesia [18, 25].

Given the specific of SEMSs, early complications after SEMS implantation include sore throat, chest pain, death, severe cough, hemorrhage, and airway perforation [10, 11, 26‐28]. In this series, 19 patients had minor bleeding during stent placement that was successfully controlled with bronchoscopy compression. Compared to the uncovered stents, covered stents showed a higher rate of sore throat or chest pain, which probably resulted from the self-expanding force that facilitates the stent to attach directly to the airway wall. With respect to late complications, granulation tissue formation had been reported around stents with a frequency of 12–46% [4, 5, 18]. In our study, there was a relatively high incidence of granulation tissue formation (34.35%) during the median period of 1276 days, which may be attributed to larger quantity of patients and longer follow-up time. Previous studies have shown that the incidence and degree of granulation tissue hyperplasia may be related to a multitude of factors, such as the pressure of the stent on the wall, the friction of the airway wall, and local airway infection [29]. However, the etiopathogenesis of granulation in SEMSs is still unclear, and more data and prospective studies are needed.

The total complication frequencies in our research are analogous to those reported in previous studies [5, 7, 9, 21]. SEMS-related hyperplastic tissue formation and restenosis caused by hypertrophic scar tissue can be managed with various flexible bronchoscopic interventions when necessary [9]. In our study, time-to-granulation tissue formation of covered and uncovered stents was about twenty days. SEMS-related complications should be managed promptly after stents insertion. These complications require interventions by experienced bronchoscopists who have mastered interventional techniques such as balloon dilation, electrocautery, and other therapies.

The optimal duration for placement of the temporary metallic stent still remains controversial. Chen et al. suggested that the optimal placement time for a covered stent is between 2 and 6 months [30]. In our study, the survival time of covered and uncovered stents was a median of 25 and 1339 days, respectively. Rodriguez et al. indicated uncovered metal stents have a theoretic advantage of neo-epithelialization that stent could incorporate into the airway wall [31]. However, the neo-epithelialization could also be a cause for concern if granulation tissue produces a recurrent obstruction inside the stent [26]. Our records did not demonstrate this problem because the stent had been selected based on the type of disease before being implanted. Most patients in our study had airway malacia or cicatricial stenosis; thus, uncovered stents were selected. There were 44 (78%) patients who maintained patency with neo-epithelialized stents out of the 66 total patients who had uncovered stents inserted during a median follow-up period of 1276 days (range: 2–4263 days).

According to our experience, sedation and local anesthesia are adequately prepared before bronchoscopy. Sedation with intravenous midazolam (5 mg) and a local anaesthetic with 2% xylocaine solution were administrated prior to bronchoscopy [6]. During the operation, if the patient has a cough or movement, the 2% xylocaine was sprayed in the trachea. Because non-availability of fluoroscopic guidance, we used a guidewire to provided direct visualization of stent placement, which ensures the accuracy of stent position. While, the technique required an experienced bronchoscopist to ensure safety of patient.

There were several limitations to our study. First, it was a retrospective study of a single center, the outcome measures were not well-defined and there was the possibility for missing data from the retrospective review. Therefore, future prospective controlled studies are needed. Second, several of our patients were lost to follow-up and could not be evaluated for long-term success. Third, it may be difficult to clarify the complex factors contributed to complications, even though our study reported a higher frequency of granulation formation after SEMS deployment in patients with benign tracheobronchial stenosis. Consequently, long-term prospective multicenter studies are needed to clearly define clinical indications for airway stenting and its therapeutic value in selected patients.

The placement of a self-expanding nitinol stent achieved most clinical improvement among patients in our study. Implantation of SEMSs for treatment of benign airway stenosis was reliable. The high rate of resolution can be achieved with further intervention. Although SEMS-related complications are inevitable, adequate endotracheal measures can be used to address them. Our experience verifies that using permanent SEMSs for benign tracheobronchial stenosis is effective and safe for the majority of patients in a long-term follow-up.