The clinical presentation is dependent on the severity of airway obstruction and on cardiopulmonary reserve. Typically, patients remain asymptomatic until stenosis exceeds 50%. Effort tolerance is first affected because the pressure drop across any obstruction increases with increasing airflow velocity. Symptoms at rest often only present when tracheal lumen narrowing is ≤5 mm. As a result of being relatively asymptomatic despite the presence of severe airway obstruction, these patients may only be first identified when a precipitant such as infection, edema, or mucous impaction triggers a life-threatening airway occlusion.

A high index of suspicion is needed if the patient presents with a history of prior endotracheal intubation or tracheotomy, tuberculous endobronchitis, gastroesophageal reflux disease, or systemic illnesses such as Wegener’s granulomatosis or relapsing polychondritis. Wheezing refractory to bronchodilator therapy and recurrent pneumonia are classical presentations, and stridor or unilateral wheezing on physical examination is a clear indication for airway evaluation. Hypoxia or hypercapnia may not be present even in the presence of severe dyspnea.

Computed tomography (CT) can provide valuable anatomical information on the location and extent of the lesion. However, standard axial imaging provides limited information on the length of obstruction, the relationship to adjacent mediastinal structures, and the presence of malacia. Therefore, multi-planar imaging with three-dimensional reconstruction and dynamic expiratory CT is preferred (Fig. 26.3).

Spirometry may yield classical flow-volume loop patterns of upper airway obstruction (Fig. 26.3), but sensitivity is low, and the typical flow loop cutoffs are not seen until the tracheal lumen is narrowed to <10 mm. Hence, normal spirometry does not rule out the diagnosis of airway obstruction in any patient in whom it is suspected and bronchoscopic evaluation is still warranted. Although there may be some role for spirometry in objectively documenting physiological severity of lesions, this evaluation can be confounded by obstructions at multiple sites and by comorbid airway disease such as chronic obstructive pulmonary disease (COPD). Furthermore, spirometry is a demanding investigation on patients who are in respiratory distress, and they are often unable to produce either satisfactory or reproducible measurements.

Bronchoscopy is the diagnostic modality of choice in all airway obstruction. However, the timing is debatable with some endoscopists recommending initial, routine flexible bronchoscopic evaluation of all referred cases as opposed to deferring airway inspection to the time of treatment with rigid endoscopy. Flexible bronchoscopy may be dangerous in patients with severe airway obstruction because the obstruction can be worsened by the bronchoscope physically occluding the limited airway. However, this problem can be overcome in some cases by using ultrathin or pediatric scopes. Respiratory failure may also be exacerbated by moderate sedation. Therefore, any attempt at bronchoscopy must be undertaken in a setting with a skilled endoscopist, appropriate personnel, and facilities for advanced airway management including emergency tracheotomy. Any doubt about the ability to secure the airway should prompt evaluation with a rigid ventilating bronchoscope that has the advantage of enabling the endoscopist to concurrently control ventilation and examine the airways. Larger instrumentation is also possible with more options for therapeutic intervention, and flexible bronchoscopy can still be performed via the rigid barrel to examine the lobar and segmental airways.

Bronchoscopy enables detailed evaluation of lesions, patency assessment of airways distal to the obstruction, and examination of mucosa for evidence of active inflammation. Biopsies can be taken if the diagnosis is uncertain. However, bleeding from endobronchial biopsy, which is usually self-limiting, can in some instances exacerbate airway occlusion. Rigid bronchoscopy provides a safer option for the biopsy of central vascular lesions by securing the airway, offering superior suction capability, and enabling direct tamponade of any bleeding sites.

A standard classification system for airway obstruction has yet to be established, and this can prove a major hindrance to communication in a multidisciplinary team. One recently proposed system by Freitag et al. improves precision and interobserver agreement by classifying stenosis as either structural or dynamic and then further subdivides lesions by location, degree of stenosis, and transition zone. Although other staging systems of laryngotracheal stenosis have been previously devised and correspond with surgical outcomes, these systems are heavily weighted to the location of the lesion and are limited in application to only the upper trachea.

In the classification system, structural stenosis is classified into four groups: intraluminal occlusion, extrinsic compression, distortion, or scar (Fig. 26.4). Dynamic stenosis is defined by >50% airflow obstruction in expiration and is categorized as either cartilage malacia or a floppy posterior tracheal membrane (Fig. 26.5). Cartilage damage results in a saber-sheath trachea if the lateral walls are weak, a crescent-shaped trachea if the anterior walls are weak, and a circumferentially occluded trachea if both anterior and lateral walls are involved. In contrast, excessive dynamic airway collapse involves only the bulging of the floppy posterior wall. It typically involves the lower trachea and main stem bronchi. Endoscopic quantification of the degree of any dynamic stenosis needs to account for confounding variables such as patient position, depth of sedation, and the use of respiratory maneuvers in functional bronchoscopy.

The location of the pathology is described to be in the upper, middle, or lower third of the trachea or in either main stem bronchi (Fig. 26.6). The surgical implication is that up to half the upper and middle trachea can be resected, but the length of resection is limited to 40 mm at the level of the carina. Measurements in relation to normal airway landmarks such as the vocal cords, cricoid cartilage, carina, and major bronchial bifurcations provide greater accuracy in defining location. These measurements should be made from the top, as well as from the bottom of the lesion. A lesion is considered a simple stenosis if confined to a single cartilage ring without any associated malacia or chondritis. Complex stenoses are more extensive in length (Fig. 26.7) and are complicated by cartilage damage. They often have poorer results with endoscopic intervention.

The degree of endoluminal occlusion is categorized as <25%, 26–50%, 51–75%, 76–90%, and 90% to complete obstruction (Fig. 26.8). The severity is measured at its worst point in the respiratory cycle, and this usually occurs at the end of expiration. Transition zone refers to the abruptness of change of the airway obstruction which can be sudden as in web stenosis or more gradual and shaped like a bottleneck in cicatricial lesions (Fig. 26.9).

Laryngeal competence, involvement of the cricoid cartilage, presence of inflammation or malacia, and adequacy of distal airways should also be assessed during initial bronchoscopy. These factors will affect results with endoscopic intervention and may mandate an early surgical referral. Moreover, if a nonfunctional larynx is not recognized preoperatively, patients will need further tracheotomy or endotracheal intubation even after tracheal surgery. The technique of surgical management of subglottic stenosis (between vocal cords and lower border of cricoid cartilage) is different from the treatment of pure tracheal stenosis which makes identification of the cricoid cartilage in relation to the lesion essential. The cricoid cartilage lies proximal to the first tracheal ring and is the only complete cartilaginous band with no posterior muscular membrane (Fig. 26.10). Treatment results also improve if intervention occurs after airway inflammation has been allowed to resolve and the extent of the resultant scar clarified. Surgery is rarely indicated for inflammatory or infectious airway lesions because of the unpredictable natural history. Granulation, edema, and friable mucosa indicate inflammation, while pure fibrous lesions are completely covered with normal mucosa (Fig. 26.11). Temporizing solutions such as dilation can be sought to “buy” time for a stenosis to mature before proceeding with definitive intervention. The quality of distal airways for adequacy of surgical anastomosis is an obvious consideration of preoperative planning, and inspissated secretions distal to obstructions should be drained to avoid infection.