55: Endoscopic Treatments for Benign Major Upper Airways Disease

In highly selected patient populations, flexible and rigid endoscopic (endobronchial) management offers effective treatment options for benign major airway disease (e.g., stenosis and malacia). These treatments are associated with less morbidity than traditional surgical interventions. Selection criteria focus primarily on candidacy for more definitive surgical therapy, as patients can be deemed inappropriate candidates for classic resection/reconstruction for a variety of reasons: etiology, extent of disease, failed prior operation, confounding medical comorbidities, and patient preference. Lack of technical expertise at a given institution also may be a factor. Since each institution carries its own bias with respect to these parameters, a patient determined inoperable at one center, in fact, may be considered a reasonable candidate at another.

Clearly, some individuals will benefit greatly from less invasive management of their airway disease. Only rarely is acute life-threatening airway compromise (≥75% luminal compromise) encountered in clinical practice. Moreover, as an alternative to tracheostomy, immediate endoscopic palliation of a high-grade stenosis may be part of a treatment strategy that ultimately incorporates an elective staged resection.

Symptomatic subglottic and tracheal stenoses and tracheomalacias are indications for endoscopic therapy in benign upper airways disease. These etiologies are listed in Table 55-1. Whether used as the primary therapy or as an adjunct to definitive surgery, the goal of endobronchial intervention is to restore airway patency and to provide a durable response, while limiting morbidity. Procedures often involve collaboration between surgeons and interventional bronchoscopists. Critical elements of endoscopic treatments are appropriate patient selection, choice of a specific endobronchial intervention based on indication, focused postoperative care (often including steroid therapy and mucolytics), and anticipation of possible repeated interventions.

The goal of the endoscopic approach is to preserve the respiratory epithelium, while minimizing radial thermal and mechanical injury to the airway. Many procedures can be performed through an adult flexible bronchoscope (video or fiberoptic), although because of the frequent requirement for rigid bronchoscopy, skill with rigid instrumentation is mandatory and must be actively maintained. General anesthesia is generally indicated, although it is possible to perform limited interventions in a bronchoscopy suite with conscious sedation and topical analgesia. Availability of a suitable procedure room (interventional bronchoscopy suite) or an operative room to perform interventions is essential. The suite should contain several high-resolution monitors, endobronchial ultrasound capability (EBUS), mobile flexible bronchoscopy towers, and fluoroscopic capability.

The subglottis lies between the vocal cords and the proximal trachea. Congenital subglottic stenosis generally presents early in life and is characterized by an audible biphasic stridor or a persistent or recurrent croup-type cough. Historically, congenital subglottic stenosis required tracheotomy in over 40% of patients as an early palliative maneuver.¹

Acquired subglottic stenosis is commonly associated with antecedent trauma, either externally (e.g., blunt-force injury to the anterior neck) or, more frequently, internally. There is little doubt that this process represents an important, often delayed, morbidity of laryngotracheal intubation. Internal airway injury can occur as a result of direct mucosal trauma sustained during intubation, endotracheal tube cuff pressure ischemia and mucosal necrosis, constant tube motion and mechanical abrasion, and associated tracheitis.² Percutaneous dilatational tracheostomy and laryngotracheal reflux also have been implicated.³

Acquired systemic diseases such as amyloidosis, papillomatosis, tuberculosis, and granulomatosis with polyangiitis (GPA), formerly Wegener's granulomatosis, also may include subglottic stenosis as a component of the patient's symptom complex. There is also a rare idiopathic/cryptogenic syndrome, seen almost exclusively in younger women, that manifests as an obstructing subglottic web.^4,5

Fortunately, congenital causes of benign tracheal stenosis are quite rare and include extrinsic narrowing or incomplete development secondary to vascular rings or partial vascular slings. Acquired diseases account for the majority of occurrences. Specifically, intrinsic injuries caused by endotracheal intubation or tracheotomy are the most common and best characterized. Table 55-2 summarizes the four most common locations related to posttracheotomy stenosis.^2,6,7 Healing from direct trauma to the airway can result in a complex, asymmetric scar that can be difficult to palliate. The classic “A-Type” deformity (as opposed to the normal C shape of the trachea) can result from anterior collapse of the proximal trachea at the site of a prior tracheostoma. In addition, some stenoses are accompanied by tracheomalacia, which further complicates their management.

Numerous techniques can be used to relieve central airway stenosis (Table 55-3). Historically, rigid tracheoplasty (dilatation) was the first option for high-grade proximal airway narrowing. More recently, however, although rigid instrumentation is still a critical element in the management of these conditions, endoscopic treatments have become far more common because of the improved optics of flexible bronchoscopes and the development of a vast array of therapies that can be easily used through them. In addition, since a reduced skill-set is required for flexible approaches, dissemination has occurred quite rapidly. Often procedures become an amalgam of both flexible and rigid techniques as rigid scopes provide ventilatory support and stable airway access, whereas flexible scopes are passed within them and provide improved optics.

By far the most common endobronchial intervention, dilatation is seldom performed without another therapy. Depending on the complexity of the stenosis, however, repeated endobronchial dilatations alone may be sufficient to effectively palliate an inoperable airway stenosis. Bougienage (passing a series of graduated bougie tubes through a suspension laryngoscope) is an effective therapy for most simple (web-like) stenoses of the subglottis and proximal trachea. Since the tubes are relatively compliant, this form of rigid tracheoplasty is gentler on the airway than a rigid bronchoscope used to affect the same result. As the complexity of the stenosis increases (i.e., asymmetric, denser scar, component of malacia, and lengthier), rigid tracheoplasty alone becomes far less effective, and its use may lead to significant airway injury. Consequently, prior to any intervention, a thorough assessment of the pathology is mandated.

Unintended disruption of the airway can occur during dilatation because mechanical forces may not be equally distributed during rigid dilatation. If the membranous airway is spared by the pathology, it will be the point of least resistance and may split during the procedure while leaving the stenosis intact. Other weak points in the airway are the membranous–cartilaginous junctions which can dislocate during an undirected rigid dilatation. This potential problem often is overcome by pretreating the stenosis with ablation therapy to create a more controlled dilatation (see below).

With the development of graduated endobronchial balloons, pneumatic tracheoplasty can be performed bronchoscopically. Although this is a seemingly less traumatic approach, endobronchial balloons are inflated well above atmospheric pressure during dilatation, and if used improperly, are no less traumatic than standard rigid dilatation. However, because pneumatic dilatation can be performed more precisely and in a much more gradual fashion, the results are more predictable and often better.

Thermal energy to disrupt or ablate diseased tissue has been used for over 50 years. Its application within the respiratory system was limited until more recently as technologic advancements have facilitated access. A number of delivery vehicles now are available for airway applications. For benign airway stenoses, there are two main goals of ablative therapies. First, endoscopic resection and vaporization of obstructing granulation tissue or scar can be accomplished. Second, dense focal scars can be incised to create pathways of least resistance so that subsequent rigid or pneumatic dilatations can be more predictably and safely performed.

Several energy sources can create thermal injury and result in tissue ablation. The choice of source depends on the nature of the stenosis, and includes location, cause, thickness, and length of airway involvement. Having the gamut of technologies is essential. The spectrum of ablative interventions, as well as flexible and rigid video bronchoscopes (telescopes) should be available within the designated interventional suite.

Laser

The development of lasers with short wavelengths that can be transmitted through thin quartz filaments has made endoscopic application possible. The carbon dioxide laser operates at a longer wavelength (10.6 μm), which limits its use to superficial structures.⁷ The neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, however, operates at wavelengths one-tenth as long, making it the more common source. Fine fiberoptic fibers can be passed through the working channel of a standard flexible bronchoscope and can be manipulated with a high degree of accuracy. Stenoses can be endoscopically resected primarily by vaporization of tissues. Since Nd:YAG laser light is poorly absorbed by both water and hemoglobin; it penetrates more deeply into surrounding tissues than other ablative therapies. Accordingly, the risk of airway perforation and injury to adjacent structures is higher. However, the wider energy dispersion field results in effective coagulation.⁸

A rare but important complication of endoscopic ablative therapies is airway ignition.⁸ This is more commonly associated with laser procedures performed through the flexible bronchoscope than through a rigid scope. Reduction of inspired FIO₂ to <40%, avoidance of flammable endotracheal tubes (although there currently is no “laser-safe” endotracheal tube on the market), and use of reinforced endotracheal tubes or LMA are preferred during any thermal procedure. Awareness of this rare complication is critical.

Electrocautery and Argon Plasma Coagulation

Endoscopic electrocautery (diathermy) offers the ability to rapidly snare and remove large granulomas or polyps bypassing the tedious process of vaporization. Alternatively, cautery can be used similarly to the laser. Risk of airway ignition is slightly less with electrocautery because less heat is generated by electrocautery device. The depth of penetration of the thermal injury depends on contact time with tissues and, consequently, is perhaps, slightly better controlled with electrocautery than with other thermal devices.

The flow of electrons through tissues generates heat for coagulation because of the high resistance within the target tissue. Electrocautery probes require direct contact with the target tissue to initiate this effect. Argon plasma coagulation (APC) uses ionized argon gas to conduct electrons into the target, providing a noncontact mode of treatment (lightning effect).⁸ Argon gas flows flexibly, and therefore, can travel in a nonlinear fashion to the desired target (i.e., bend around corners). Moreover, as tissues are coagulated, their intrinsic resistance rises, redirecting the argon beam to adjacent, nontreated, lower-resistance tissues.⁸ This feature distinguishes APC from the laser. Also, APC can treat more superficial tissues than either laser or diathermy. Argon gas is pressurized and there is some small risk of gas emboli reaching the systemic circulation if the tip of the APC probe is kept too close to an active bleeding source.

Cryotherapy

Cryotherapy has been commonly used in dermatology, otolaryngology, and gastroenterology applications. More recently it was introduced for endobronchial treatment of both malignant and benign lesions. The mechanism of action is cellular necrosis caused by intracellular crystallization from freeze–thaw cycles.^9,10 Initially, there can be some edema following therapy, but subsequent sloughing of treated tissue (with or without balloon dilatation) results in recanalization of the airway lumen. There is very little bleeding encountered at the time of cryoablation, and the resulting microvascular thrombosis permits only minimal delayed bleeding even after tissue is sloughed and regardless of concomitant or subsequent balloon dilatation.¹¹

Histological analysis posttreatment has shown sloughing of the epithelium and deeper tissues to include the submucosal glands with preservation of the connective tissue. This appears to reepithelialize the radial margin of the injury.¹² The use of this therapy has been limited by the cryoprobe design, which was somewhat cumbersome. Recent advances have included development of noncontact cryotherapy with liquid nitrogen. This permits more uniform application of the cryogen.¹² Given the advances in this technology, conventional probe-delivered cryotherapy is useful for debulking endoluminal masses (benign and malignant), treating asymmetric scar, and foreign-body (and retained clot) extraction. Importantly, cryotherapy has no potential for airway fire. Spray cryotherapy is currently under active investigation, although its introduction into practice will be complicated by the need for highly pressurized cryogen (liquid nitrogen) which may lead to gas emboli and pneumothorax.

Microdebrider Therapy

Microdebrider therapy is another newer modality useful in the endoscopic management of subglottic and tracheal cicatricial stenosis and malignant or granulation tissue-related airway obstruction. A microdebrider is a rotary cutting tool that attaches to a suction source that simultaneously debrides and evacuates tissue to recanalize the obstructed airway. Recently, this device has become popular for removing obstructing subglottic glands, airway papillomas, tracheal scars, as well as obstructing airway cancers.¹³ The suction component of the device continually clears debris and maintains visualization of the lumen. Nevertheless, the limitations of the technology remain accidental injury to normal tissue and bleeding from the raw debrided surface which may ultimately require thermal (or cryo) cauterization.⁹ The microdebrider probe must be passed through a rigid scope and visualized with a telescope or flexible video bronchoscope. This current setup does reduce the degrees of freedom of microdebrider movement.

Topical Agents

In addition to the above-described endoscopic modalities, topical agents have been used as an adjunct to dilatational and ablative strategies. Topical endoscopic application of mitomycin C (~0.4 mg/mL) appears to be a safe and moderately efficacious adjuvant therapy, although limited experimental¹⁴ and clinical data^15-17 exist. Mitomycin C can be applied topically to the treated areas, and surprisingly, this does not appear to affect epithelial regrowth; rather, it mainly interferes with refibrosis.¹⁰ Treated areas should be surveyed regularly for squamous metaplasia. Similarly, some data support the use of intralesional steroid therapy to modulate the local inflammatory process, and this may have some benefit in the management of tracheal stenosis.¹⁸ It is common to use mitomycin C and intralesional steroids alternately during chronic endoscopic palliation of a recurrent tracheal stenosis. Although the data is scant on these topical treatments, no appreciable complications have been reported in the literature.

Successful endoscopic management of benign central airway stenosis involves a combination of endobronchial therapies. As discussed previously, dilatation alone generally is insufficient to provide meaningful palliation. After identifying the appropriateness of the candidate for therapy, control of the airway is the initial step. Usually, general anesthesia will be required. Although rare, conscious sedation may be sufficient for some patients. The airway can be controlled by suspension laryngoscope (Fig. 55-1), rigid bronchoscope (Fig. 55-2), endotracheal tube, or laryngeal mask airway (LMA). The choice is predicated on location, etiology, and magnitude of the stenosis. For high-grade stenoses, rigid control of the airway is preferred and can be changed to endotracheal tube or LMA once the airway has been partially recanalized and safely controlled. If a subglottic lesion exists, suspension laryngoscopy provides excellent access. Open tracheostomy supplies should always be close at hand in case a surgical airway is emergently required.

Patients are ventilated with intermittent apnea or jet techniques, and permissive hypercapnea is surprisingly well tolerated by most patients. Ventilating rigid bronchoscopes are useful for this purpose. A thorough assessment of the airway is made, and if more than a simple web-like stenosis exists, an ablative therapy usually will be required. The choice of ablative therapy is often guided by availability at a given institution. Laser, electrocautery, APC, and cryoprobes are designed to fit within the working channel of a standard adult bronchoscope.¹⁹

Ablative therapies are used for three different purposes. Endoscopic photoresection (i.e., laser and electrocautery) is reserved for dense cicatricial stenoses (Fig. 55-3) or obstructing granulation tissue. The obstruction is vaporized or charred then debrided with biopsy forceps. Radial incisions (i.e., laser and electrocautery) (Fig. 55-4) can be made along suspected lines of tension to help guide the direction of fracture of the stenosis during subsequent dilatation (Fig. 55-5). Care should be taken to avoid making these incisions on the membranous trachea. Two or three full-thickness incisions are made after the orientation of the airway has been established, and either endoscopic pneumatic dilatation or rigid dilatation follows. Endoscopic coagulation (APC) is used to treat diffuse superficial processes, such as benign polyposis. Regardless of the therapy, airway perforation and ignition are risks.

Regardless of etiology, limited surgical procedures exist for long-segment central airway malacia. Consequently, endoscopic and endobronchial therapies have emerged as the main therapeutic options for these difficult-to-treat functional airway stenoses. Principal among these therapies is endobronchial stenting. Internal airway stents are ideal for airway collapse because they provide support for airway structures irrespective of the cause of malacia. Unfortunately, stents themselves can lead to numerous complications related to migration and host foreign-body reactions. For long-segment and intractable malacia syndromes, T-Tube placement as a destination therapy is reasonable and serves as an important option for these unfortunate patients.

In the context of benign disease, stents can be deployed as primary treatment for malacia or as an adjuvant after benign stenoses have been ablated. There are numerous stents from which to choose, although it is now apparent that silicone stents, as opposed to metallic stents, should be used for the treatment of benign disease.²⁰

Placement of most silicone stents requires rigid bronchoscopy and general anesthesia.²¹ Careful preoperative airway measurement is required to properly size the stent. To this end, a chest CT scan with three-dimensional reconstruction of the airway is useful. Patients usually are treated with steroids to reduce the chance of bronchospasm during and immediately after the procedure.

It is important to schedule frequent follow-up visits for patients with endobronchial stents. Follow-up visits should include surveillance flexible bronchoscopy. This is necessary because stent-related complications such as migration, mucous impaction, and granulation tissue occur frequently. All patients should be managed with mucolytic therapy (via nebulizer) two or three times daily. Patients also should be instructed that for any decline in respiratory function or development of a new wheeze, medical attention should be sought immediately. Asphyxia can occur with stent migration or occlusion.

Endoscopic therapies are critical for the comprehensive management of benign airway stenosis and malacia. A multidisciplinary team, including airway surgeon and interventional pulmonologist, is necessary to identify candidates and perform procedures. An institutional commitment to secure appropriate instrumentation and technical support is also required. The threshold for transferring complex patients to more experienced centers should be low.

Every thoracic surgeon should be familiar with the techniques for endoscopic management of obstructed airways with flexible or rigid bronchoscopes. Each institution should have a minimum supply of flexible and rigid endoscopes available, as well as at least one or two of the other modalities summarized in Table 55-3. The type of modality may vary based on the experience of the hospital and the surgeon, as well as financial considerations. The more options and surgical experience the center has to offer, the better it is for patients. Elective patients should be referred to centers of excellence where sufficient expertise exists.

As rigid bronchoscopy becomes less common, surgeons should practice to maintain their skills. In cases where it is difficult to identify the vocal cords with the rigid scope, consider placing a guidewire or small intubating bougie down the airway via an LMA and use it to guide the rigid scope.