Central airway obstruction (CAO) is the narrowing of central airways (trachea, mainstem bronchi, and bronchus intermedius) due to benign and malignant diseases. In this chapter we focus on CAO due to benign diseases; it is important to note that “benign” here refers to the cause of the CAO (not caused by malignancy), but the consequences of benign CAO can be devastating and not benign in nature. The etiology of benign causes of CAO can be grouped into several large categories: mechanical/iatrogenic, inflammatory, infectious, dynamic, and idiopathic. The management of benign CAO depends on the etiology, type of lesion, and patient’s characteristics.
Benign CAO can be classified into simple and complex. Simple CAO lesions are less than 1 cm in length, shaped like a web, and have no associated malacia or damage to cartilaginous tissue. Complex CAO lesions are longer than 1 cm, can involve the cartilage, and have more complex shapes like hourglass or irregular thickening.
Etiology of Benign Central Airway Obstruction
Airway complication rates after lung transplantation range from 2% to 33%. Complication rate is related to surgical technique, donor ventilation time, donor bronchus length, donor-recipient height mismatch, and prolonged periods of ischemia. Airway complications from transplantation include bronchial infection, necrosis, anastomotic dehiscence, fistula formation, granulation tissue, malacia, stenosis, or complete obstruction of the airway (vanishing airway). The location of the lesion can be at the anastomotic site or distal to it.
Postintubation/posttracheostomy tracheal stenosis (PITS/PTTS) are manifestations of mechanical injury to central airway. PITS usually develops due to prolonged intubation (>7 days) with an overinflated cuff (pressure >20 cm H 2 O). PTTS occurs due to cartilage damage during initial tracheostomy, infection, bleeding, or an overinflated cuff.
Chemical injury to the airway can result from a variety of caustic gases (hydrochloric acid, ammonia, aldehydes), thermal injury from fire exposure in poorly ventilated areas, and pill aspiration (such as iron, potassium chloride, metformin). These injuries result in tracheobronchitis and extensive airway mucosal sloughing that ultimately leads to granulation, stricture, and stenosis.
Relapsing polychondritis (RP) is an immune-mediated disease that targets cartilage (collagen type II, IX, XI) in the eyes, ears, nose, joints, and large airways. Both malacia and stenosis can occur. RP spares the posterior tracheal membrane because it has no cartilage. The resulting tracheobronchomalacia/excessive dynamic airway collapse can be focal or diffused.
Tracheobronchopathia osteochondroplastica (TO) presents as calcified nodules due to accumulation of calcium phosphate in the airway cartilage. These lesions are characteristically located on the cartilages only. They are mainly asymptomatic and found incidentally but can be extensive in some patients and can lead to symptomatic airway stenosis.
Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated necrotizing granulomatous vasculitis that can lead to airway inflammation and stenosis. The airway involvement is usually more resistant to systemic treatment.
Sarcoidosis is a systemic nonnecrotizing granulomatous disorder that almost always involves the pulmonary system, including the airways. Stenosis can occur due to unchecked inflammation. Enlarged lymph nodes may cause extrinsic compression and airway stenosis.
Inflammatory bowel disease (ulcerative colitis and Crohn’s disease) can lead to a necrotizing granulomatous infiltrative process in the airways that may result in inflammation and stenosis.
Amyloidosis results from extracellular amyloid fibril deposition that is usually due to a beta-pleated sheet conformation of proteins. Light chain amyloidosis is due to plasma cell dyscrasia. Amyloid A amyloidosis is due to chronic inflammation with excess amyloid A deposition. Airway involvement is notable for infiltration and stenosis.
Recurrent respiratory papillomatosis (RRP), due to human papillomavirus (HPV) type 6 and 11 (with potential to transform to squamous cell cancer), presents as papilloma that can affect the entire upper and lower airways; the characteristic appearance is a “bunch of grapes.”
Tuberculosis (TB) can cause endobronchial infection that can appear in various forms bronchoscopically, including edematous-hyperemic, fibrostenotic, tumorous, granular, or ulcerative form. Endobronchial TB usually involves lobar airways and airways >2 cm in length. These airway lesions can be highly contagious, and bronchoscopy should be done with strict respiratory precautions when TB is suspected.
Fungal infections ( Aspergillus , Fusarium , mucormycosis, and Cryptococcus ) can also present as airway stenosis. The presentation of fungal infection–related airway stenosis is extremely variable, and so care and caution should be noted when evaluating CAO to ensure ruling out concurrent fungal infection.
After exclusion of all other causes, the diagnosis may be idiopathic subglottic stenosis—a disease that usually affects middle-aged women who also suffer from gastroesophageal reflux disease. Idiopathic CAO usually involves short segments of the subglottic area and can be recurrent over many years.
Patient presentation is dependent on etiology and severity of CAO. Commonly, patients will report dyspnea on exertion that can progress to shortness of breath at rest, wheezing, or stridor. Patients may also develop chronic cough or recurrent respiratory infections due to inability to clear secretions at the site of CAO. The degree of dyspnea typically correlates with the diameter of the affected airway, with dyspnea on exertion appearing when central airway luminal size is less than 25% to 50% of normal, with stridor occurring at a lumen less than 5 mm in diameter.
Pulmonary Function Tests With Flow-Volume Loops
Flow-volume loops can help differentiate CAO into three functional groups (fixed, variable extrathoracic, and variable intrathoracic) and may help with characterizing the CAO diagnosis. These are illustrated in Fig. 15.1 .
Computed tomography (CT) of the chest is a critical component to both diagnosis and treatment planning for benign CAO. High-resolution CT (0.6–1-mm slices with overlap) allows for accurate evaluation of the length and extent of the stenosis, assessment of the extraluminal component, and determination of distal airway patency. High-resolution CT also enables custom/ personalized stent design in appropriate situations. If dynamic airway pathology is suspected, then CT images in both the inspiratory and expiratory phases should be performed.
Bronchoscopic evaluation of CAO should be done with the goal being to fully characterize the lesion (visual evaluation and measurement) and determine if there is a reversible component such as infection (via washing, needle/brush/forceps biopsy).
A stand-alone diagnostic flexible bronchoscopy can be the first step, but it is discouraged if the airway stenosis is severe; if the lesion is severe, a simple diagnostic bronchoscopy can turn into an airway emergency, so the ability to escalate the level of care if required, even if doing a “simple” diagnostic bronchoscopy, is important. Often it is better for the interventional pulmonologist to perform one bronchoscopic evaluation that is both diagnostic and possibly therapeutic, starting with a flexible bronchoscope but with the rigid bronchoscope standing by, so that if warranted the procedure can be switched from diagnostic to therapeutic intervention as warranted.
Benign central Airway Obstruction Management
Successful benign CAO management rests on three fundamental principles. First, a multidisciplinary approach to the disease is essential to ensure all treatment modalities are considered. Thoracic surgery, otolaryngology, and interventional pulmonology should all be involved. Second, systemic treatment of the underlying disease is often more effective than local bronchoscopic treatment alone, so an integrated therapeutic approach is often warranted. Finally, in patients with minimal to no symptoms, it is often best to resort to a watchful waiting approach as interventions may make the lesion worse by precipitating additional inflammation and trauma.
Dilation of the airway stricture can be accomplished using a balloon or rigid bronchoscope. Various types of balloons are available for dilation in the airway. The key is to use a balloon of the appropriate diameter and length. The diameter of the balloon is selected based on the airway size proximal to the stenotic segment as measured on CT scan. The length of the balloon is typically at least 0.5 cm longer than that of the stenotic segment, thus flanking the stenosis. Time of inflation is usually 30 s to 120 s. Repeated dilation and longer duration of dilation are suggested if the patient is able to tolerate the longer inflation times. Caution should be exercised in benign airway disease, as some airways can be very inflamed and fragile, and overdilation can result in rupture across a large area. It is usually prudent to start dilating with smaller balloons and then progressively increase balloon diameters during subsequent dilations as the airways permit, making sure to reassess tissue effects after each dilation. Never inflate the balloon against significant pressure that can be felt by the assistant inflating the balloon and communicated to the operator.
Of note, a rigid bronchoscope can be used as a dilation tool. In order to circumvent the need for repeated intubation of the patient, the operator can use a larger rigid tracheoscope to intubate the patient, then remove the universal head from the scope and insert smaller but longer rigid ventilating scopes through the tracheoscope. Smaller rigid ventilating scopes are used to dilate the stricture initially. Subsequently, progressively larger rigid ventilating bronchoscopes are passed through the rigid tracheoscope and across the stenotic segment. This telescope technique allows for ventilation and sequential dilation without the need for repeated intubation through the vocal cords.
Radial cuts at 4, 8, and 12 o’clock location using an electrocautery knife or lasers (neodymium-doped yttrium aluminum garnet [Nd:YAG], potassium titanyl phosphate [KTP], carbon dioxide [CO 2 ]) can be performed prior to balloon dilation for tight, circumferential strictures. These cuts allow for more effective dilation ( Fig. 15.2 ) of simple weblike strictures.