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Computed Tomography Measurements for Airway Stent Insertion in Malignant Airway Obstruction

Righini, Christian MD, PhD* † ‡; Aniwidyaningsih, Wahju MD‡ §; Ferretti, Gilbert MD, PhD‡ † ∥; Pra, Yves MD; Raymond, Christel Saint MD§; Ferretti, Katharina MD; Hustache, Claire PharmD; Diab, Samia MD§; Reyt, Emile MD* ‡; Pison, Christophe M. MD, PhD‡ §

Journal of Bronchology & Interventional Pulmonology: January 2010 - Volume 17 - Issue 1 - p 22-28
doi: 10.1097/LBR.0b013e3181ccadbe
Original Investigations
Free

Background Metallic airway stents for malignant airway obstruction are considered safe, yet are not without complications. This study reviews the role of computed tomography (CT) airway measurements for planning stent placement in malignant airway obstruction before the actual therapeutic procedure to avoid invasive diagnostic evaluation before the stent placement and to reduce complications.

Methods This study is a retrospective review of information from a stent order database and medical records of patients receiving stents for malignant airway obstruction at a university hospital over a 12-year period. CT scans were used to determine stent diameter by calculating mean diameters of healthy adjacent zones (proximal and distal), stent length (length of diseased airway), and location and number of potential stents. Results of CT planning before bronchoscopy were judged by complication rates.

Results Patient population consisted of 69 patients, 61.7±14.0 years old, 40 males, in whom 92 stents were inserted. The most frequent cause of airway obstructions was tracheobronchial cancer (32). All patients had nitinol stent placement; 66 stents were covered and 26 were uncovered. Follow-up time was 1 to 1067 days (median: 35 days). Complication rate was 10.1% and mainly involved the patients with tracheal obstruction (6). Complications included stent fractures (2), migration (2), granuloma (1), and infectious tracheitis (2). One early death within 24 hours after the procedure was not related to stent placement. Five patients required follow-up therapeutic bronchoscopy to treat the complications.

Conclusions These results suggest that prestent planning by noninvasive method of obtaining CT scan provides optimal stent size and position, possibly avoiding a diagnostic bronchoscopy and reducing complications. Further prospective study is needed to confirm these results because of limitation of this study's design.

*Clinique d'Oto-Rhino-Laryngologie, Pôle tête et cou et Chirurgie réparatrice

§Clinique de Pneumologie, Pôle de Médecine Aiguë et Communautaire

Pôle Imagerie

Département d'Anesthésie Réanimation

Département de Pharmacie, CHU de Grenoble

InsermU823, Epidémiologie des cancers et affections graves, Institut Albert Bonniot

Université Joseph Fourier, Grenoble, France

Reprints: Christophe M. Pison, MD, PhD, Pôle de Médecine Aiguë et Communautaire, Clinique de Pneumologie, Centre Hospitalier et Universitaire de Grenoble, BP 217 X, 38043 Grenoble Cedex 9, France, and Université Joseph Fourier (e-mail: CPison@chu-grenoble.fr).

Received for publication June 29, 2009; accepted November 17, 2009

There is no conflict of interest.

Central airway obstruction (CAO) is a major challenge for physicians dealing with thoracic malignancies such as lung and mediastinal cancers. Most patients suffer from dyspnea, obstructive pneumonia, and atelectasis and they can often face life-threatening situations. Although many interventions have been developed, mortality and morbidity from CAO remain high.1–3

The decision to intervene in malignant CAO patients is mainly determined by the patient's clinical condition, underlying pathology, prognosis, physician's experience, and the availability of the equipment at each center. In patients with CAO, resectional surgery is usually contraindicated for a variety of reasons. Frequently, such patients are not even in a condition to undergo invasive diagnostic testing or repeated bronchoscopies.2,4–8

Computed tomography (CT) scan offers guidance in planning appropriate interventions in a variety of situations, thus avoiding diagnostic bronchoscopy. It could provide measurements for the length, diameter, and location of the involved airway segment, proximal and distal diameter of the healthy adjacent zones, and also the possible number of stents required. The CT scan can also provide information on whether the airways distal to the obstruction are patent or not, especially with advanced imaging (virtual bronchoscopy) as well as the relationship of the obstruction to other adjacent structures, such as major vessels.9–13

Preoperative airway evaluation is crucial in patients with CAO; CT scan of the chest can offer this information in a noninvasive manner. The goals of airway evaluation by CT before stent placement in our study were to meet 2 objectives: (1) to relieve obstruction by selecting optimal diameter, length, and location for the stent and (2) to anticipate any possible complication related to the stents, especially in healthy adjacent zones (granulation or migration). We hypothesized that by achieving these 2 goals, complication rates after stent placement could be lower and could validate our noninvasive approach before stent insertion. We reviewed the medical records of all patients with malignant CAO receiving nitinol stents at our institution.

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PATIENTS AND METHODS

This retrospective study was approved by the Ethics Committee of the Center for Clinical Investigation of our institution. This study was conducted at a university hospital. All patients recorded in our hospital pharmacy order database as having an airway stent insertion for malignant airway obstruction were reviewed. Data were collected from the electronic database and the medical records for the duration between January 1995 and May 2007 at the Centre Hospitalier Universitaire de Grenoble, France. Telephone calls were made to the patients and/or their relatives to get most recent updates of the patient's condition. For the patients who could not be reached by telephone, the last appointment date for surviving patients was considered as the censored date.

The diagnosis of airway obstructions was confirmed by symptoms, physical examination, and radiologic imaging. Bronchoscopy before stent insertion was performed only in patients without established pathologic diagnosis and never only to determine the characteristics of the lesions or to obtain the dimension of the potential stent. In all cases with known or unknown cause of obstruction, we confirmed the diagnosis of CAO first by the CT scan.

We did not use any scoring system to determine improvement in dyspnea because there were no data on this variable in the medical records or the electronic database; instead, we used recorded respiratory support before and after the procedure as an indirect parameter of symptom improvement. We classified respiratory support into 4 categories from breathing room air to oxygen therapy by cannula/mask, noninvasive ventilation, and invasive ventilation. We do not have complete pulmonary function testing in all patients because most of the patients were unable to perform expiratory maneuvers because of their advanced stage of cancer.

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CT Planning and Airway Measurement

Helical CT, including monodetector CT, and then multidetector CT (4 then 16 slices) since 2004 were used to image the central airways. Acquisition of the data was performed using either 3-mm or 1-mm slices, 100 to 120 kVp, and 80 to 150 mA. Images of the entire central airway were acquired within 5 to 17 seconds, according to exiting CT technology. Coronal reconstructions in parallel with the main axis of the trachea and bronchi were generated as well as sagittal reconstructions, and all measurements were performed on the CT monitor. All patients in this study underwent CT measurement for a potential stent placement before any interventional procedure was carried out. We defined “healthy adjacent zone” as airway feasible on CT images that was considered as normal morphology without any mass distortion or apparent reduction of normal diameter and without any fistula formation. These parameters were based on the study by Ferretti et al,14 which showed good correlation between CT imaging and of bronchoscopic findings, except in 20% cases with moderate stenosis.

The diameters of the adjacent healthy patent airway zone proximal and distal to the obstructed airway were measured in the axial plane as 2 orthogonal diameters. The stent diameter (D) was the mean between

as described in Figure 1A. The diameters of the proximal adjacent healthy zone

FIGURE 1.

FIGURE 1.

and diameter of the distal adjacent healthy zone

are shown in Figure 1B. The length of the obstruction was also measured on coronal and sagittal reconstructions and 10 mm were added at the proximal and distal ends of the obstruction to determine the length of the stent to be used

The optimal positioning and the number of potential stents required were also determined during this evaluation by considering the obstruction's location and length. The 10-mm addition at both ends is used to ensure that the stent will cover all the diseased part and prevent migration. Figure 2 depicts a case that was evaluated preoperatively using the above method and provides images after stent placement and chemotherapy.

FIGURE 2.

FIGURE 2.

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Stent Placement

All patients in this study were not suitable for resectional surgery and were treated with nitinol stent placement (Ultraflex Microinvasive, Boston Scientific, Watertown, MA). The early cases up to 2000 were treated under local anesthesia and using a flexible bronchoscope BF P40 (Olympus Optical, Tokyo, Japan). Subsequently, we used a rigid ventilating bronchoscope (Φ7.5 Karl Storz, Tuttingen, Germany) or flexible bronchoscope with intravenous general anesthesia in the operating theater. These procedures could also be combined with other procedures such as balloon dilatation, mechanical debulking, electrosurgery, and laser photoresection as indicated. Stent deployment was carried out by introducing a guidewire into the barrel of the rigid bronchoscope or through the flexible bronchoscope channel and the stent was released under direct observation.

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Monitoring Complications

The monitoring of complications of the procedure was carried out by evaluating any new respiratory symptoms that were recorded in the patients' medical records and by telephone calls to patients or their relatives or to referring physicians. Follow-up imaging studies were only carried out if any new symptoms occurred and were suspected as complications or disease progression that might require further intervention. In case of difficulty interpreting the symptoms after a careful evaluation of the CT images, a flexible bronchoscopic evaluation was performed. Flexible bronchoscopy was never performed only for surveillance purposes after stent insertion.

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Statistical Analysis

Statistical analysis was performed using SPSS software (Statistical Package for the Social Sciences Software Release 11). Significance was determined through Wilcoxon rank test, P value <0.05 was considered significant, and survival analysis was evaluated by using Kaplan-Meier analysis.

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RESULTS

Over the study period from January 1995 to May 2007, 69 patients were included in our study (40 males, 29 females), aged 61.7±14.0 years, who underwent 92 stent insertions (66 covered, 26 uncovered). The diagnoses of airway obstruction and their location that required stent placements are summarized in Table 1. Most airway obstructions were caused by tracheobronchial cancers (32) followed by esophageal cancer (19), thyroid cancer (9), mediastinal malignancy (6), and other malignancies (3, 1 of each—pulmonary sarcoma, distant metastasis from malignant melanoma, and endometrial carcinoma).

TABLE 1

TABLE 1

The location of the obstruction was mainly tracheal (Table 1) and stent placements were also mostly in the trachea (43 patients). There was a decrease in the level of respiratory support after stent placement but this was not significant (P=0.06) (Table 2). Duration of follow-up ranged between 1 and 1067 days, with a median of 35 days, and median survival time of these patients was 3.7 months.

TABLE 2

TABLE 2

Complications that followed stent placement were stent fractures (2), migration (2), granuloma (1), and infectious tracheitis (2), with a median of 91 days' duration between stent placement and the development of the first complication. Most complications occurred with tracheal stents (6) whereas 1 incident of migration took place in the case of tracheobronchial stent. Further interventions, such as electrosurgery, laser photoresection, and mechanical debulking, were required in 5 patients after complications occurred. All complications occurred more than 48 hours after stent placement. There was 1 death within 24 hours after stent placement because of the advanced stage of the disease and was not considered related to the procedure.

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DISCUSSION

Airway stents are kept in position by radial force applied against the airway wall, and therefore excessive force to the airway wall may induce bronchial ischemia, irritation, granuloma formation, hemoptysis, rupture, or other complications.15 In contrast, if an undersized stent is placed there will be less force applied to the airway wall with risk of migration. Thus, choosing the “optimal” diameter, length, location, and number of stents is crucial.

The decision on which size stent to be used (diameter and length) and how to determine the size of the stent varied between centers. Some centers routinely perform a diagnostic bronchoscopy before stent placement. This is done to evaluate airway patency beyond the obstruction and for measurement of the length of the lesion, by withdrawing the tip of the scope from the distal to the proximal end of the stenosis and measuring the scope movement. This means submitting patients to an invasive diagnostic procedure before the definitive treatment. We attempted to avoid this diagnostic procedure by using CT planning prior to the actual therapeutic procedure.16–18 Other centers determined the diameter of the stent by measuring diameter of the lumen in relation to the barrel of the endoscope or to the opening of biopsy forceps.19,20 Madden et al21 used flexible and rigid bronchoscopy to size relevant airway portion before the stent was used and the diameter of the stent was matched to the diameter of the normal proximal lumen.

Our method used a mean orthogonal diameter proximal and distal to the healthy adjacent zone as stent diameter, and the length of obstructed airway with the addition of 10 mm at the proximal and distal end was considered as stent length. By considering these 2 objectives, complications such as migration, granuloma formation, or stent fracture could be reduced. We believe that our method prevented “over” or “under” sizing of the stent, thus curtailing complications compared with that published in the literature.

We found no complications during the follow-up within the first 48 hours after the stent placement and a low complication rate of 10.1% 48 hours after the procedures. Five patients, who had complications, were successfully treated with interventional procedures such as electrosurgery, laser photoresection, mechanical debulking, and cryotherapy, with or without stent replacement. Patients experienced a decreased need for respiratory support after stent placement although the improvement was not statistically significant (P=0.06). Figure 2 shows a CT scan of a patient with respiratory distress because of airway invasion secondary to a tracheal and right main bronchus neoplasm.

In our study, we found stent fractures and migration as the most common complications yet only in 2 cases each. Moreover, we avoided a diagnostic procedure just to gauge the size of the stent. We believe that CT scan of the chest can avoid invasive diagnostic procedures prior to stent placement for determining diameter, length, position, and number of potential stents. We tried to compare these complication rates with other studies as follows.

Madden et al21 have followed up the outcome of nitinol airway stent placement in benign and malignant airway obstruction. They had 5 cases of malignant airway obstruction among 15 patients who had more than 1 year follow-up and 2 of them had complications (granuloma, metal fatigue, and halitosis). Saad et al,18 who used Wallstent and Ultraflex stents, reported complications in 17 patients among 50 cases of malignant obstruction, for example, granuloma (4%), infection (10%), migration (4%), and hemoptysis (16%) with a median follow-up 42 days. Husain et al22 have studied the long-term effects of stent placement in benign and malignant airway stenosis. They have found, in a short-term follow-up (<48 h after placement), 10 complications among 54 patients with malignant obstruction and 8 complications in 48 patients after more than 48 hours after stent placement, with a median survival of 128 days. The occurrence of migration in our study was also found in 2 cases (2 of 69) and in comparison with an earlier study by Saad et al,18 these complications seem to be less frequent.

We found granuloma formation in 1 case (1 of 69) and it is not a frequent occurrence but it could be because of the length of the observation period and the fact that our cancer patients were in an advanced stage of the disease. Our study had 2 cases of infections after stent placement and they were successfully treated with antibiotics. Table 3 shows the comparison summary between several studies of nitinol stent in malignant airway obstruction.

TABLE 3

TABLE 3

Cough was the complication that most commonly occurred during tracheal stent placement (6 cases) and there was only 1 case of migration in the case of tracheobronchial placement. Mechanical receptors in the airway are concentrated in the larynx, trachea, and carina and become less frequent in distal airways. Stent placement in a tracheal site can induce cough more frequently compared with more distal placement and this may be the probable cause of complications found mostly in tracheal stent placement.23

Routine surveillance by bronchoscopy after stent placement was not performed in our hospital because we wished to avoid any invasive procedure, especially in patients with advanced conditions, and we monitored the patients by observing whether any new complaint could be due to a complication from the stent placement. Matsuo and Colt24 found that routine surveillance with bronchoscopic evaluation after stent placement did not detect a high incidence of stent-related complications among patients without the occurrence of new respiratory symptoms. A follow-up study after stent insertion by Ferretti et al25 has also suggested that CT is an accurate noninvasive method that can be used for the evaluation of stent placement.

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CONCLUSIONS

Tracheobronchial measurement by CT imaging may give a better evaluation of the “optimal” sizing (length and diameter), location, and number of stents required. This may have led to better results as seen in our study by reducing complications because of stent placement. These preliminary data suggested that prestent planning by noninvasive method with CT scan will give the optimal stent size and position. We could avoid invasive procedures before definitive treatment decisions are made, especially in severe cases and debilitated patients. The limitation of our study is that it is retrospective in nature and does not involve comparison with any other method for the sizing of the metallic stents. There is also the possibility that some complications were overlooked because of the design of the study, which was carried out over a 12-year period of observation. However, we feel that with the encouraging results of low complications, such a study should be carried out in a prospective, multicenter manner.

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ACKNOWLEDGMENTS

The authors thank research technicians Mrs Joane Ferran and Caroline Tournegros, who are involved in the data management, and Mrs Hélène Barre, who is in charge of stent logistics in our hospital. Dan Veale, MD, FRCP, corrected the English text.

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Keywords:

malignant airway obstruction; computed tomography scan; nitinol stent; complication

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