LARYNX, HYPOPHARYNX, AND CERVICAL ESOPHAGUS

KEY POINTS

Computed tomography is the primary imaging examination for evaluating the nature and extent of iatrogenic trauma and subglottic stenosis.
Computed tomography is an ideal complement to clinical and endoscopic examinations.
Swallowing studies are still sometimes useful.
Imaging may reveal complications of therapy that might threaten airway integrity in patients treated for airway problems.

INTRODUCTION

Etiology

Subglottic stenosis is a common complication of intubation or tracheostomy placement. It is by far the most commonly encountered iatrogenic injury to the larynx (Fig. 208.1). Other less common iatrogenic causes of laryngeal stenosis are surgery related to restoration of laryngeal function in a patient with true vocal cord (TVC) paralysis and operations to improve laryngeal and tracheal stenosis following complications of intubation or trauma (Fig. 208.2). Imaging is used sporadically to assess bleeding from a vascularized free flap used in a reconstruction (Fig. 208.3) or osteoradionecrosis following RT (Fig. 208.4); the latter is discussed in Chapters 21 and 206 as it relates to the treatment of laryngeal and hypopharyngeal cancer.

Subglottic stenosis is otherwise caused by a number of noniatrogenic inflammatory, otherwise infiltrating and neoplastic conditions discussed with the laryngeal manifestations of those diseases in Chapters 202 and 204 through 206.

Clinical Presentation

Patients may have complaints of persistent pain, hoarseness, those related to aspiration and airway encroachment (dyspnea and stridor) following intubation, tracheostomy (emergent or routine) and surgery for vocal cord dysfunction, trauma, and subglottic stenosis. Throat pain is a less usual symptom.

ANATOMY AND PATHOPHYSIOLOGY

Anatomy

A thorough knowledge of the following anatomy and anatomic variations of normal in each of the following areas is required for the evaluation of iatrogenic trauma and the sometimes resulting subglottic stenosis trauma. This anatomy is presented in detail with the introductory material on the larynx, hypopharynx, cervical esophagus, and infrahyoid neck in general:

Evaluation of Primary Laryngeal Injury

Larynx, including the laryngeal skeleton, deep tissues spaces within the larynx, mucosal landmarks, and functional structures within larynx (Chapter 201)
Hypopharynx (Chapter 215)
Cervical esophagus, most importantly the esophageal verge junction with the postcricoid portion of the hypopharynx (Chapter 221)
Trachea (Chapter 209)
Visceral compartment of the neck and related fasciae (Chapter 149)

Evaluation of Related Vocal Cord Dysfunction and Nerve Injury

Knowledge of the entire course of the recurrent laryngeal nerves (Chapter 201)

Pathology and Patterns of Disease

Postintubation Injury and Subglottic Stenosis

Chronic laryngeal and in particular subglottic stenoses are mainly related to misplaced prolonged and traumatic intubation. The endotracheal tube may denude the mucosa of the glottis or subglottis either due to pressure necrosis or chronic irritation (Fig. 208.1A–E). Pressure necrosis occurs during prolonged intubation when the cuff pressure exceeds capillary perfusion pressure, causing a chain of events starting with mucosal ischemia and necrosis, eventually leading to exposure of laryngeal cartilage, chondritis, granulation tissue formation, and finally maturation into firm scar tissue (Fig. 208.5). If the balloon is inadvertently blown up in the subglottis, the effects may be worsened. The subglottic airway is particularly at risk in the pediatric airway because the subglottis is the narrowest portion of the airway in children. Unavoidable damage may be caused by emergency cricothyroidotomy. Avoidable subglottic injury can be obviated by recognizing a high tracheostomy placement through the anterior cricoid ring or one higher than the typical placement at or immediately below the second tracheal ring (Fig. 208.6). As the denuded cords re-epithelialize, webs may form and compromise the airways, limiting vocal cord mobility (Fig. 208.1F). The subglottic region may heal with proliferation of scar tissue that reduces the lumen of the airway (Figs. 208.1–208.6).

Computed tomography (CT) demonstrates the cross-sectional area of the residual airway in the subglottis (Fig. 208.2B). This measured area is the best correlate for airway functional studies and is a key factor in medical decision making. Those treating subglottic and tracheal stenosis understand that reduction of the airway luminal area leads to proportionate decrease in airflow and worsening functional capacity of the patient. In adults,, 25% reduction of airway cross-sectional area usually causes few symptoms. A 25% to 50% reduction causes dyspnea with fairly extreme exertion, while a 50% to 75% reduction might produce dyspnea with mild exertion. A .75% reduction may cause symptoms at rest and audile stridor. The time course of any airway obstruction is also critical. Acute airway obstruction is much more poorly tolerated than a more chronic, progressive process.

FIGURE 208.1. Computed tomography (CT) study in a patient suffering chondritis from a traumatic intubation. The initial study in the active phase of chondritis was done without contrast. The follow-up study was done with contrast. A–E: This study was done following intubation because of progressive upper airway obstruction and vocal cord dysfunction, and it shows extensive soft tissue swelling (arrows) throughout the larynx from the true vocal cord level through the low subglottis. In particular, the inflammatory tissue produced extensive erosion of the posterior aspect of the cricoid cartilage. There is also fairly extensive swelling surrounding the larynx (arrowheads). F–I: The contrast-enhanced CT study done after treatment shows essentially complete resolution of the active inflammatory tissue with residual scarring. In (F), there are postinflammatory webs at the anterior and posterior commissure (arrows) resulting in an abnormally medial location of both arytenoid cartilages (arrowheads). Residual nonactive scar tissue is present in the area of cricoid cartilage erosion (arrow in G), and there is some soft tissue scarring that narrows the subglottic airway (arrow in H). Persistent areas of demineralization of the cricoid cartilage remain (arrowheads in H).

FIGURE 208.2. A patient suffering airway obstruction and increased vocal cord dysfunction following injection of the left true vocal cord with Teflon to treat an idiopathic left vocal cord paralysis. The volume of injected material was far too great. A: While part of the left true cord was medialized, the injection spread deep to the conus elasticus to occlude more than 50% of the subglottic airway. B, C: The method of calculation of the degree of encroachment on this subglottic airway is demonstrated (C).

FIGURE 208.3. A patient who had a vascularized free flap to reconstruct the pharynx following total laryngectomy. There was evidence of bleeding into the neopharynx. A single image from the computed tomography angiographic study shows puddling of contrast in the neopharynx (arrows).

FIGURE 208.4. Subglottic stenosis due to radiotherapy (RT) can occasionally be significant; usually it is minimal and functionally inconsequential. A: This patient can be seen to have had a very extensive laryngeal carcinoma with gross cartilage destruction. The patient refused total laryngectomy and was treated with RT. B: There is .75% persistent narrowing of the subglottis due to postradiation edema and scarring. C: The thyroid cartilage can be seen to have healed. The patient was cured of cancer by the RT, but the larynx remained essentially useless and the patient was tracheostomy dependent for the rest of his life.

FIGURE 208.5. Subglottic stenosis can be associated with various imaging appearance as it evolves. It can also be classified as soft tissue, cartilage, or combined stenosis. Three patients are shown in various stages of evolution of subglottic stenosis. All patients had computed tomography studies. A–D: Patient 1. In (A), there is subtle soft tissue swelling along the posterior wall of the subglottis (arrow) showing a nonenhancing component due to either edema or possibly end-stage fibrosis, while the arrowhead shows enhancing tissue consistent with ongoing inflammatory, likely granulation, tissue. In (B), the enhancing component (arrow) and nonenhancing component of the soft tissue changes are more extensive. In (C), the enhancing component can be seen involving the cricoid cartilage (arrows) compared to the normally mineralized cartilage (arrowhead). In (D), there is interarytenoid/ posterior commissure scarring that resulted in secondary vocal cord dysfunction due to this postintubation subglottic stenosis. This patient was treated with multiple laser resections of the abnormal tissue. The white line circles the expected dimension of the low subglottic airway as the denominator for the calculation. The red line outlines the residual lumen, which would be the numerator for the calculation of residual airway lumen area and subtracting that from 100% would give the degree of airway area reduction. Such a calculation is possible in almost all patients, as can be observed in subsequent illustrations in this chapter. E, F: Patient 2 showing a subglottic stenosis narrowing the airway to about 25% of its usual cross-sectional measurement due to scarring and a cartilaginous stenosis, especially posteriorly. G–I: Patient 3. This patient had postintubation subglottic stenosis and was treated with multiple laser excisions and some attempts at mitomycin application. The larynx was finally stented with a bone graft between the inferior margin of the thyroid cartilage and the anterior cricoid arch. In (G), the nonenhancing scar circumferentially narrows the subglottis to .50% of its usual cross-sectional area (arrow). Abnormal enhancing tissue surrounds the strut bone (arrowhead) that was being slowly resorbed. Sagittal reformatted images in (H) show the remaining eroded residual strut bone. The sagittal image suggests that the subglottic airway is not significantly reduced. Sagittal viewing of the larynx can be very misleading in this regard. The arrowheads show the top and bottom of the cricoid cartilage so that the region of the subglottis is identified. There is a small amount of narrowing seen on the posterior wall just across from the strut. On the coronal image in (I), the airway narrowing in the subglottis is more apparent by judging the amount of soft tissue between the medial margin of the cricoid cartilage (arrows) and the soft tissue border with the airway (arrowheads). (NOTE: Both coronal and sagittal views as well as anteroposterior and lateral plain films can be deceiving with regard to estimating subglottic airway dimensions. This is why axial imaging and calculations as demonstrated in Figure 208.2C are a better way to assess the degree of airway encroachment and correlate that with reduced functional airway capacity.)