Fig. 12.1
Postracheostomy tracheal stenosis
Percutaneous tracheostomy is a procedure that is increasingly indicated in the critically ill patient, and it is associated to the development of tracheal stenosis as well.
A publication on 100 patients that underwent percutaneous tracheostomy revealed that major postoperative complications presented in 2.4% of cases, and these included death, cardiac arrest, loss of the airway, pneumothorax, tracheoesophageal fistula, and injury to the posterior wall of the trachea (mucosal tear). The rate of minor complications such as bleeding or cellulitis is presented in 1.8% of cases. Tracheal stenosis was reported in 31% of patients, 20% of which were symptomatic [21].
Long-term complications of percutaneous tracheostomy are infrequently mentioned in the literature; however some published data suggests that the rate of tracheal stenosis is significantly higher than reported [22].
VanHearn et al. showed that of 80 decannulated patients after percutaneous tracheostomy, an index of stenosis greater than 10% was found in 26% of them, being moderate in 4% of the cases and severe in 2% [23].
Another study evaluating 214 of 356 patients with percutaneous tracheostomies revealed that 8 of them (3.7%) developed symptomatic tracheal stenosis [24].
Infectious
Many airway infections can cause damage to the tracheal mucosa, resulting in stenosis. Tuberculosis (TB), fungal infections, bacterial tracheitis, histoplasmosis, and diphtheria are some of them, with TB being the most frequently seen.
Tuberculosis is the most common infectious cause of airway stenosis. It usually produces distal stenosis (at the level of the bronchi), but central airway stenosis can also occur. This complication can present at the time of the active infection or long after that, up to 30 years [25]. The most important risk factor for developing airway stenosis is the presence of tuberculous bronchitis, which is found in 10–37% of patients with pulmonary tuberculosis when bronchoscopy is performed [25, 26]. In those cases, over 90% of patients will develop tracheobronchial stenosis in spite of correct TB treatment [27].
Infectious stenosis is more prevalent in underdeveloped countries, particularly in Asia and Africa. Active infection produces necrosis and ulceration of the bronchial mucosa, giving rise to granulation tissue and subsequent fibrous stenosis.
During fibrous, established stenosis, dilatation of the lesion is an option. When the stenosis occurs at bronchial level, balloon dilatation can be offered. At tracheal level, rigid bronchoscope dilatation is useful as well. Repeated dilatations or stent placement are often required, since recurrence rate is very high.
Idiopathic Tracheal Stenosis
The term idiopathic tracheal stenosis (ITS) is used to include patients with tracheal stenosis when all other etiologies have been investigated and ruled out. It is thought to be a result of an inflammatory process of unknown etiology. Since location and general characteristics are similar to inflammatory or cicatricial tracheal stenosis, the investigation of potential causes has to be exhaustive before this term is applied.
ITS is a rare condition, characterized by circumferential fibrous stenosis beginning at the subglottic area and compromising the proximal segment of the trachea. It typically affects women on their third to fifth decade and presents with months to years of symptoms such as progressive dyspnea, wheezing, stridor, or a combination of all of them. In many cases patients are misdiagnosed as difficult to treat asthmatics [28].
Grillo et al. [28] presented 49 patients with tracheal stenosis where no etiology was found after extensive evaluation. A retrospective review of records showed that radiologic studies were still available in only 15 of the 49 patients with ITS. All 15 patients had radiographs and plain tomographies, and one patient had a computerized tomography scan of the neck.
Review of the available information showed that idiopathic laryngotracheal stenosis produced focal, 2–3 cm long stenosis at the cervical trachea. The lumen was severely compromised, measuring no more than 5 mm in diameter at its narrowest portion. The stenosis was concentric or eccentric, presenting either smooth or lobulated margins.
Grillo’s report highlighted the need to pay special attention to the airway in chest radiographs or computerized tomographies when evaluating a patient with a history of prolonged dyspnea and wheezing. It is also important to consider ITS in the differential diagnosis of patients with focal narrowing of the airway.
A recent multicenter study described 23 patients, 96% of which were women aged 45 ± 16 years, endoscopically treated for ITS. Time between first symptoms and diagnosis was 19 ± 18 months. Bronchoscopy showed weblike (61%) or complex (39%) stenosis, located at the upper part of the trachea, mainly at the cricoid cartilage area.
Endoscopic treatment included mechanical dilation only (52%) or associated with laser or electrocoagulation (30%) and stent placement (18%). All procedures were efficient. Follow-up after endoscopic therapy was 41 ± 34 months, showing recurrence of ITS in 30% of patients at 6 months, 59% at 2 years, and 87% at 5 years. Treatment of recurrences (n = 13) included endoscopic management in 12 cases [29].
Bronchial Stenosis Post Lung Transplantation
Since the first lung transplant in 1963, technical advances in thoracic surgery along with new immunosuppressive agents have made lung transplantation a more common indication for those patients with terminal lung disease. However, one of the main problems of this surgical procedure is the development of stenosis at the level of the suture.
Perianastomotic stenosis occurs in 12–40% of patients and nonanastomotic distal bronchial stenosis in 2–4% of all lung transplants [30, 31].
Bronchial stenosis is related to airway inflammation, with mononuclear cell injury to the epithelium and mesenchyme that is further complicated by endothelial injury on a poorly vascularized area. The severe blood-flow impairment may lead to bronchial cartilage ossification, calcification, or fragmentation, leading to stenosis [32].
Other risk factors increase the risk for suture stenosis, such as the use of a simple suture and prolonged mechanical ventilation. There is a very high risk of suture infection also due to low blood flow and the presence of inflammation. Infection should be looked for and appropriately treated before performing any endobronchial manipulation, particularly if a stent placement is considered.
Success depends primarily on the experience of the interventional pulmonology team and the medical resources available.
Distal Bronchial Stenosis
As mentioned previously, bronchial stenosis secondary to pulmonary tuberculosis is quite common. Approximately 43% of patients with pulmonary tuberculosis will develop stenosis at the distal bronchi [33, 34] (Fig. 12.2). This number corresponds to approximately 4.1% of all bronchoscopies performed in a hospital.
Fig. 12.2
Bronchial stenosis: right upper lobe
As a result of bronchial stenosis, there exists difficult drainage of secretions and recurrent infections distal to the obstruction, with the development of bronchiectasis. In these situations, it is indicated to offer a dilatational therapy that can be performed via balloon dilatation with or without laser application. This treatment is simple to apply and can be easily performed during a short procedure. It has good results, improving secretions clearance which in turn prevents repeated infections. In addition to bronchoscopy, three-dimensional helical tomography of the tracheobronchial tree can be very useful in the evaluation of this condition, since it allows a better distal inspection than bronchoscopy [37].
Another less common cause of airway stenosis is radiation therapy. The incidence of bronchial stenosis has increased following treatment with brachytherapy or external beam radiotherapy of malignant lesions of the airways, with an estimated incidence of 9–12% [38].
Bronchial stenosis is established within an average of 40 weeks after initiation of radiotherapy. Bronchoscopy can show the presence of a whitish-colored membrane covering the mucosa, with important inflammatory response that ultimately results in fibrous stenosis [38]. Radiation therapy rarely compromises the tracheal mucosa.
Diagnosis Methods
Patient History
Due to the broad range of etiologies and the non-specific nature of presentation, the diagnosis of airways stenosis may be delayed in time. A careful medical history should be obtained in patients suspected of airway stenosis, since background data is very important. Prior infectious diseases, history of airway intubation, prolonged mechanical ventilation, timing and severity of dyspnea, presence of dysphonia, etc., should be recorded and evaluated.
Symptoms develop gradually as progressive dyspnea until tracheal stridor appears; this could happen in most of the cases, when the diameter is affected around 70% (diameter around 5 mm in size).
When patients present emergently, it is important to offer a therapeutic procedure to reopen the airway to avoid worsening of symptoms and serious complications such as respiratory failure or respiratory arrest. The goal of treatment is to restore and maintain patency of the airway as soon as possible, and then a multidisciplinary team can decide which is the best long-term solution for a given patient.
In clinical practice, most of the patients present with symptoms of stenosis when they are in the fibrous phase of the stenosis, with minimal evidence of inflammation. They frequently have a history of a prior airway intubation or prolonged mechanical ventilation in the past. Many patients have been diagnosed and treated for difficult to control asthma, with minimal or no response to asthma therapy.
A significantly smaller number of patients will present within days or weeks from extubation, and in those cases an important airway inflammation can be seen.
Onset of symptoms is very variable. In a work of Marquette et al. describing 58 patients with airway stenosis, 5 of them developed symptoms within 5 days, 23 patients presented symptoms from 5 to 30 days of extubation and 19 patients from 30 to 90 days, and 8 patients took more than 90 days in presenting symptoms. Half of them went to the emergency room with acute respiratory failure [39].
The auscultation of wheezes, especially a fixed one, indicates that the passage of airflow through the airway is reduced, but its location does not always correlate with the site of airflow obstruction. That means that when a fixed wheeze is heard over the trachea, it does not necessarily indicate that the source of the obstruction is the trachea [40]. When wheezing is unilateral, it often suggests an obstruction of the airway distal to the carina.
The persistence of a fixed unilateral wheezing should always warrant bronchoscopic examination, paying special attention to the distal airway (segmental or subsegmental bronchi). Stridor is always a sign of severe laryngeal or tracheal obstruction and occasionally main bronchial obstruction.
Imaging Techniques
In the study of tracheobronchial stenosis of the airway, noninvasive imaging techniques have an important role. They help not only in diagnosing but also in deciding the most appropriate treatment and assessing response to therapy during the follow-up period. These techniques have developed significantly in recent years [41] allowing a better approach to airway stenosis.
Simple chest-X rays are rarely diagnostic of central airway obstruction.
Computed tomography (CT) has been the most commonly used imaging test for diagnosis and evaluation of airway stenosis in order to have better information of the length and size of the stricture, degree of destruction of the airway wall, surrouding organ injury and also to have images control after treatments (Fig. 12.3a, b).
Fig. 12.3
(a–c) Tracheal stenosis and CT scan with reconstruction in 3D
Although very useful, CT has some limitations particularly in the evaluation of subtle airway stenosis in axial images, underestimation of the craniocaudal extent of the disease, and generation of a large number of images for review [42].
The introduction of multiplanar reformatting (MPR) CT scans with option to generate three-dimensional (3D) images and virtual endoscopy (VE) provide additional information regarding airway pathology [43] bringing visual data that closely resemble the images obtained from flexible bronchoscopy [44].
MPR CT scan allows the acquisition of thin-slice axial sections of entire body volumes during a single breath-hold, thus eliminating respiratory artifacts [45].
This technique provides information on the length and caliber of the stenosis and the degree of compromise of the laryngotracheal wall. It allows visualizing lesions in depth, showing thickening or thinning of the tracheal wall, fibrous involvement of the submucosa, or disappearance of the tracheal rings. Also, the relationship of the injury to adjacent organs can be better evaluated.
Virtual endoscopy (VE) is a reconstruction technique that exploits the natural contrast between endoluminal air and the surrounding tissue [46], allowing navigation through the tracheobronchial tree with the same endoluminal perspective as an endoscopy [44] (Fig. 12.4).
Fig. 12.4
Tracheal stenosis. Virtual bronchoscopy
Several authors have demonstrated the high diagnostic accuracy, sensitivity, and specificity of noninvasive, multirow detector CT virtual endoscopy in evaluating and grading central and segmental airway stenosis and its close correlation with flexible bronchoscopy [43, 46–48]. However, it is slightly more accurate at assessing central airway stenosis than segmental airway stenosis [46].
The combination of axial imaging, multiplanar reformatting, and three-dimensional rendering is useful prior to tracheal intervention, especially when there is significant anatomical distortion or airway narrowing [47].
Recently, some authors advocate the use of MRI for diagnosis localization and extension of tracheal stenosis. MRI is a noninvasive procedure without ionizing radiation and can be used to identify the relationship of the trachea to adjacent vascular structures and to determine the degree and length of tracheal stenosis in high-resolution imaging with excellent soft-tissue contrast and without applying ionizing radiation or intravenous contrast medium.
Unfortunately, standard MRI has a limited ability to show dynamic organs.
The use of real-time, dynamic, cine MRI (CMRI) can achieve better results showing the mobility of the organs identified [49].
Bronchoscopy
Flexible bronchoscopy remains the primary diagnostic technique in the study of inflammatory tracheal stenosis and is considered the gold standard procedure for this pathology, allowing direct visualization of the airway lumen and sampling (biopsies). However, when the patient is in acute sever symptoms, flexible bronchoscopy is best avoided due to the risk of precipitating acute or complete airway obstruction. In these cases, the best approach has to be rigid bronchoscopy.
Moreover, bronchoscopy offers information at different levels and can assess the mobility and morphology of the vocal cords and arytenoids in subglottic laryngeal stenosis. In tracheal stenosis, it allows location of the lesion and evaluation of the degree and length of the stenosis and notes characteristics such as the presence or absence of malacia, mucosal involvement in inflammatory disorders, granulomas, ulcerations, or established fibrosis. It also enables obtaining biopsies, a procedure that should always be performed in tracheal stenosis, to rule out other inflammatory conditions. Bronchoscopy is a minimally invasive procedure, with the additional advantage of not exposing the patient to ionizing radiation. One limitation of this technique is the inability to evaluate the distal airways in severe stenosis, since the bronchoscope cannot be further advanced from the stenotic area. In these cases, sedation during the procedures and the use of an ultrathin bronchoscope with external diameter of 2.1 mm help bronchoscopists to explore tracheobronchial tree beyond the stenosis since the bronchoscopy is better tolerated.
Figure 12.5a–c shows how bronchoscopy permits the correct evaluation of the distance from vocal cords to stricture, the length of the stricture, distance from stenosis to main carina, and the degree of compromize of the cricoid cartilage.
Fig. 12.5
Vision of flexible bronchoscopy permits the correct study of the distance from VC to stricture, length of the stricture, distance from stenosis to main carina, and affectation of the cricoid cartilage
New bronchoscopic technologies, however, permit a more accurate assessment of the airway wall structure and characterization of the stricture before, during, and after treatment, since the correct evaluation of tracheal wall structures is necessary for optimal management of tracheal stenosis.
Endobronchial ultrasound (EBUS) has been introduced as an adjunct to diagnostic bronchoscopy. Radial EBUS helps evaluating the different tracheal and bronchial wall layers, as well as parabronchial structures. Cartilage damage can be better assessed, influencing the type of treatment that will be offered [50]. Also EBUS could asses differences in central airway wall structure in patients with various forms of expiratory central airway collapse who can be identified by endobronchial ultrasound using a 20 MHz radial probe [51] (Fig. 12.6.).
Fig. 12.6
Central airway wall structures: endobronchial ultrasound (EBUS)–histology correlations. (a) The five layers of the cartilaginous wall and the three layers of the membranous area of the bronchial wall are revealed by EBUS using a 20 MHz radial probe. (b) Laminar structures of the cartilaginous wall as seen on histology and the corresponding hypo- and hyper-echoic layers seen with EBUS. [51] with permission
Optical coherence tomography (OCT) is a new bronchoscopic imaging technique that has generated considerable interest since it has a much better space resolution than computed tomography. It is capable of generating high-resolution cross-sectional images of complex tissue in real time.
Similar to ultrasound, OCT measures backscattered light intensity using coherence interferometry to construct topographical images of complex tissue. It can provide a micron level, real-time image of the airway wall structure with a resolution approaching histology [52]. It offers a unique combination of high-resolution (1–15 mm) and in-depth penetration of 2–3 mm that is adequate for imaging superficial airway anatomy and pathology. OCT has the potential to increase the sensitivity and specificity of biopsies, create 3D images of the airway to guide diagnostic procedures, and may have a future role in different areas such as the study of tracheal stenosis. Some authors hypothesize that this technology may in the future provide a noninvasive “optical biopsy” [53], helping, as we said, in diagnosis and treatment of a number of conditions (Fig. 12.7).
Fig. 12.7
OCT application of OCT image for measurement of tracheobronchial stenosis. CT scan (a) and bronchoscopic (b) image of LMB (left main bronchus) stenosis. OCT images of normal bronchial lumen before (c) and after (e) the bronchial stenosis (d). OCT allows accurate measurements pre (f) and posttreatment (g) with balloon dilatation. (Courtesy Dr. Lam and Dr. Shaipanich from BCCA)
Anatomic optical coherence tomography (aOCT) , a modification of conventional OCT, is a novel light-based imaging tool with the capacity to measure the diameter and lumen area of the central airways accurately during bronchoscopy. This technique can measure tracheal stenosis dimensions, having good correlation with chest CT scan findings and guiding the selection of a proper-sized airway stent [54]. Standard OCT also could obtain accurate measures of stenosis.
All these new technologies are very promising, and they are currently under active research to define their proper role in the study of airway conditions.
Though flexible bronchoscopy and the different imaging techniques have shown to be useful and reliable in the diagnosis of tracheobronchial strictures, they all have technical limitations that can lead to an inaccurate characterization of airway stenoses [55]. The best way to evaluate these conditions is to combine different diagnostic approaches in order to correctly define the injury and then plan the best procedure, case by case, based on clinical, endoscopic, and radiological findings.
Pulmonary Function Test
Regardless of the cause, tracheal stenosis causes increased airway resistance and decreased flows. A simple test such as spirometry can help in diagnosing and characterizing a central airway stenosis. The shape of the flow-volume curve (F/V) obtained by spirometry and flow resistance (raw) calculated by plethysmography can give important information. For instance, flattening of the inspiratory loop with preservation of expiratory flow represents variable extrathoracic obstruction of the central airway. In turn, compromise of the expiratory loop with a normal inspiratory limb indicates variable intrathoracic obstruction. In a fixed obstruction (intra- or extrathoracic), both inspiratory and expiratory curves are affected, presenting with a classic flattening in the F/V loop (Fig. 12.8).
Fig. 12.8
Pulmonary function test in tracheal stenosis
Another important information that can be obtained with spirometry concerns to the functional status, and helps deciding whether or not the patient is a surgical candidate.
Classification of Benign Tracheal Stenosis
Airway narrowing may result from intrinsic stenosis or extrinsic compression or for both. It has been classified following different parameters, in an attempt to design a useful algorithm for treatment.
Cotton et al. [56] in one of the first classifications of tracheal stenosis in 1984 used the cross-sectional area of the stenosis in a group of pediatric patients and divided this condition into four grades:
I: 50% obstruction
II: 51–70% obstruction
III: 71–99% obstruction
IV: Complete obstruction
In this classification, location and length are noted but without affecting the grading of the stenosis.
In 1992, McCaffrey [57] retrospectively reviewed the treatment of 72 cases of LTS. Although diameter and length were factors, the predominant predictor of outcome was location. Locations were confined to the glottis, subglottic area, and upper trachea.
Four stages were defined as follows:
- 1.
Stage 1 in the subglottis or trachea, 1 cm in length
- 2.
Stage 2 in the subglottis, .1 cm in length
- 3.
Stage 3 in the subglottis and upper trachea
- 4.
Stage 4 in the glottis with vocal cord fixation and paralysis
In 1999, Brichet and coworkers [8] proposed a classification based on four categories depending on bronchoscopic findings:
Pseudoglottic stenosis: defined as typically “A”-shaped stenosis due to lateral impacted fracture of cartilages in patients with a history of tracheostomy.
Weblike stenosis: when it involves a short segment (<1 cm).
Membranous concentric stenosis: when there is a membrane obstructing the lumen without damage to the cartilages.
Complex stenosis: all other stenoses, including those with an extensive scar (≥1 cm), circumferential hourglass-like contraction scarring, or malacia, were defined as such.
Moya et al. [58] reviewed 54 patients that underwent surgery for laryngotracheal stenosis and defined findings according to topographic and lesional criteria, incorporating three independent variables: stage of development (S), caliber (C), and length (L). Recently this classification has been modified. It is presented in Table 12.1.
Table 12.1
Classification criteria for inflammatory stenosis of the trachea
Structure (S) Structure of the tracheal wall | Caliber (C) Internal diameter (at the point of smaller diameter) | Length (L) Axis of the larynx-trachea | |||
|---|---|---|---|---|---|
S1 | Acute-subacute inflammation | C1 | >10 mm (area > 25 μm) | L1 | Stenosis ≤2 cm |
S2 | Organized scar fibrosis | C2 | 8–10 mm (area 16–25 μm) | L2 | 2–4 cm stenosis |
S3 | Malacia | C3 | ≤8 mm (area ≤ 6 μm) | L3 | >4 cm stenosis |
S4 | Tracheoesophageal fistula | ||||
In 2007 Freitag et al. [59] proposed a standardized scheme, presenting descriptive images and diagrams for rapid and uniform classification of central airway stenosis. In Fig. 12.9 classification was based on the type of lesion, degree, and location. They divided airway stenosis into structural and dynamic, and they included malignant causes as well.
The structural group has four major types:
Type 1: includes exophytic intraluminal malignant or benign tumors and granulation tissue.
Type 2: stenosis is due to extrinsic compression of all causes, including nonpulmonary tumors.
Type 3: stenosis is due to distortion, kinking, bending, or buckling of the airway wall.
Type 4: shrinking and scarring are the predominant features.
Stenoses were further classified in dynamic when a malacic condition that varied with the respiratory cycle was found. They included two different types:
Type 1: triangular (tent-shaped) benign stenosis in which the cartilage is damaged.
Type 2: it is the inward bulging of a floppy posterior membrane.
In turn, the degree of stenosis was assigned a numerical code that could be applied to any site:
Code 0: no stenosis
Codes 1: 25% decrease in cross-sectional area
Code 2: 50% decrease
Code 3: 75% decrease
Code 4: 90% decrease
They defined five locations within the central airways:
Location I: upper third of the trachea
Location II: middle third of the trachea
Location III: lower third of the trachea
Location IV: right main bronchus
Location V: left main bronchus
In 2008, other authors [7] classified airway stenosis into two groups, according to their morphological aspect in simple and complex, similar to the Brichet’s classification. Simple stenosis included granulomas, weblike, and concentrical scarring stenosis. All these lesions were characterized by endoluminal occlusion of a short segment (<1 cm), absence of tracheomalacia, or loss of cartilaginous support (Fig. 12.10). Complex stenoses were represented by a longer lesion (greater than 1 cm) with tracheal wall involvement and subsequent scarring contraction of the latter, in some cases also associated with malacia (Fig. 12.11).
Fig. 12.10
Simple tracheal stenosis
Fig. 12.11
Complex stenosis
Almost all of these classifications quantify the degree of the stenosis as a percentage, which is a subjective observation during bronchoscopy. Sometimes we can have an approximation with images such as a CT scan, but this method is not exact either since measurements vary according to the respiratory timing of image acquisition (inspiration, expiration).
In a recent report, Murgu and Colt published a study on subjective assessment using still bronchoscopic images of benign causes of laryngotracheal stenosis containing normal and abnormal airway cross-sectional areas that were objectively analyzed using morphometric bronchoscopy and classified as mild (<50%), moderate (50–70%), or severe (>70%). These images were then subjectively assessed by 42 experienced bronchoscopists participating in an interventional bronchoscopy course. Only 47% of strictures were correctly classified by study participants (mean 16.48 ± 2.8). Of the 1447 responses included in this analysis, 755 were incorrect: 71 (9%) were overclassifications of strictures’ severity and 684 (91%) were under-classifications. There was no correlation between number of strictures correctly classified and number of lifetime bronchoscopies, or number of strictures seen by bronchoscopists in an average month. As a conclusion, the authors said that: “Experienced bronchoscopists often misclassify the degree of airway narrowing when using still bronchoscopic images to subjectively assess strictures of benign aetiology” [60].
In another paper a similar survey of 123 members of AAB (American Association for Bronchology) shows that the assessment in CAO central airways obstruction is currently performed in a visual manner (91% of the consulted clinicians). Eighty-six percent of the clinicians consulted agreed that there is an urgent need to avoid subjective visual evaluation and standardize calculations during in vivo explorations [61].
This demonstrates the importance of using systems that allow us to make a more objective measurement for conducting exploration.
Murgu and Colt proposed the morphometric bronchoscopy. They use an imaging system called Image J. During the bronchoscopic procedure, different captures are taken, in the center of the proximal airway, distal and directly into the lesion. Then after the procedure, with this manual method, it is possible to calculate the stenosis index (SI) [62] (Fig. 12.12).
Fig. 12.12
Bronchoscopic photos of the idiopathic concentric subglottic stenosis (a) and the normal distal tracheal lumen (b). The calculated stenosis index (SI) was 80%. SI improved to 30% after laser and rigid bronchoscopic dilation (c). The stenosis (d) and the normal distal tracheal lumen (e) at 12 months follow-up. The calculated SI was 50%. At 18-month follow-up, the stenosis was stable with an SI of 50% (f). [62] (with permission)
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