Subglottic Stenosis


Continuing Education Activity

Subglottic stenosis can be defined as the narrowing of the upper airway, which lies between the vocal folds and the lower border of the cricoid cartilage. Causes of subglottic stenosis can be either congenital, acquired, or idiopathic. This activity reviews the evaluation and treatment of subglottic stenosis and highlights the role of the interprofessional team in the care of patients with this condition.

Objectives:

  • Describe the pathophysiology of subglottic stenosis.
  • Review the appropriate process for the evaluation of subglottic stenosis.
  • Outline the management options for subglottic stenosis.
  • Summarize the importance of collaboration amongst the interprofessional team to enhance the care of patients with subglottic stenosis.

Introduction

Subglottic stenosis can be defined as the narrowing of the upper airway, which lies between the vocal folds and the lower border of the cricoid cartilage. Normally, the subglottic lumen is 4.5 mm to 5.5 mm in a full-term neonate, while a 3.5 mm lumen is normal in a premature neonate. A subglottic diameter of 4 mm or less in a full-term neonate is considered as narrow. Causes of subglottic stenosis can be either congenital, acquired, or idiopathic. In congenital subglottic stenosis, there is no history of endotracheal intubation or any other acquired cause of the stenosis. A rare genetic disorder called Pallister Killian syndrome is caused by tetrasomy 12p mosaicism and presents phenotypically with multisystem morphologic defects involving the respiratory system and progressive subglottic stenosis.[1] 

Acquired subglottic stenosis is more common than congenital due to the introduction of prolonged intubation in the 1960s, and it does not improve with time.[2] Avoidance of tracheostomy in patients with subglottic stenosis is paramount and this is possible by advances in balloon dilation and endoscopic cricoid split techniques. Tracheostomy decannulation can be more likely with laryngotracheal reconstruction and cricotracheal resection.[3] Idiopathic subglottic stenosis is very rare and is characterized by circumferential stenosis in the subglottic region and upper trachea. A single-stage laryngotracheal resection and reconstruction are the preferred definitive treatment for idiopathic subglottic stenosis.[2] Signs and symptoms range from recurrent croup and exertional stridor to complete airflow obstruction requiring tracheostomy.[4] 

Symptoms of idiopathic subglottic stenosis can be misinterpreted as asthma. When asthma medication fails to treat symptoms, the patient is diagnosed with an endoscopic evaluation. Depending on the severity of the stenosis, the treatment can involve Grillo’s technique, cricoplasty, or a combination of resection and enlargement techniques using rib cartilage grafts.[5]

Etiology

Trauma is the most common cause of the acquired subglottic stenosis, and the trauma can be external or internal. External trauma is more common in adults and is due to roadside accidents and clothesline injuries. Internal laryngeal trauma is iatrogenic, secondary to endotracheal intubation. Intubation compromises 90% of the cases of acquired subglottic stenosis in children due to the completely cartilaginous ring in the upper airway and the pseudostratified, ciliated, columnar respiratory epithelium with loose areolar tissue in this region. The severe injury occurs after 17 hours of intubation in adults and after 1 week in neonates.

Premature infants tolerate more prolonged intubation due to more pliable cartilage and the high location of the neonatal larynx in the neck with posterior tilt and funnel shape. Endotracheal tube size should allow an air leak at 20 cm of water pressure. The safest material to use for prolonged intubation includes polymeric silicone and polyvinyl chloride. Nasogastric tubes can also cause pressure necrosis and perichondritis. Normally during the third month of gestation, the laryngeal lumen is recanalized after normal epithelial fusion is completed. However, in congenital stenosis, the recanalization fails to happen. Other causes include burns, ingestions, infection, and inflammation (gastroesophageal reflux disease, Wegener’s granulomatosis).

Epidemiology

The incidence of subglottic stenosis is reported as less than 4% in the 1980s studies and 0.6% in studies published after the 1990s. The decrease in the incidence is because of the improved handling of neonates who require ventilator support. The current incidence of subglottic stenosis is between 0% to 2%.[6]

Pathophysiology

In acquired subglottic stenosis, the endotracheal tube causes pressure necrosis at the point of interface with the tissue causing mucosal edema and ulceration. This interrupts normal ciliary flow causing mucociliary disruption and can lead to infection. Primary healing is also prevented due to mobile and loose subglottic submucosa and insufficient vascularization of the cartilage resulting in stenosis secondary to granulation tissue proliferation. Idiopathic subglottis stenosis, more specifically, is often located at the cricoid cartilage, with the narrowest part being between the cartilage’s upper edge and the first tracheal ring. This is often circumferential, though it can be eccentric.

Histopathology

The histopathology of idiopathic subglottic stenosis shows dense fibrosis of the keloidal type with interspersed fibroblasts. The overlying epithelium shows metaplasia, and the cartilaginous rings are mostly normal histologically. Estrogen seems to play a role in idiopathic subglottic stenosis, but no estrogen or progesterone receptor overexpression is seen in the disease process.[7]

History and Physical

In congenital subglottic stenosis, symptoms usually appear shortly after birth. The main symptoms are biphasic stridor, dyspnea, air hunger and suprasternal, intercostal, and diaphragmatic retractions. Abnormal cry, aphonia, or hoarseness occur when the vocal cords are affected. In acquired subglottic stenosis, there is a history of laryngeal insult, and symptoms usually occur 3 to 4 weeks after the insult.

Evaluation

Radiological evaluation: Computed tomography (CT) and magnetic resonance imaging (MRI) are useful in establishing the diagnosis of subglottic stenosis. Higher speed CT has reduced imaging timing. Radiography helps to locate the exact location and length of the stenotic segment. The anteroposterior high kilovoltage technique increases the visibility of the upper airway by enhancing the tracheal air column while deemphasizing the bony cervical spine. Optical coherence tomography (OCT) is a minimally invasive endoscopic imaging modality capable of monitoring the progression of subglottic mucosal injury. OCT and texture analysis help in the early detection of mucosal injury, which helps with better management of the airway and limits its progression to stenosis.[8] Evaluation of swallowing is a must before airway reconstruction to avoid the risk of aspiration postoperatively.

Endoscopic examination: Direct endoscopic visualization with flexible fiberoptic endoscopy assesses the dynamics of the vocal cord function and the upper airway plus the esophagus. The rigid telescope carries importance in children for better visualization of the small larynx.

Gastroesophageal reflux disease (GERD) evaluation: Gastroesophageal and gastrolaryngopharyngeal reflux plays a role in the exacerbation of subglottic stenosis and adversely affect the successful outcomes of laryngotracheal outcomes. Therefore, 24 hours of esophageal pH probe using the dual-probe technique is most reliable.

Pulmonary function tests: A useful marker to follow in patients with subglottis stenosis is spirometry. This is also indicative of post-op outcomes in airway surgery candidates. Patients with subglottic stenosis have FEV1/PEF >10. This ratio does not correlate with the anatomical severity of the stenosis in terms of the Mayer-Cotton grading system. As per a case report, low peak inspiratory flow was related to worsening airway obstruction in patients with subglottic stenosis. Some authors use spirometry values as a noninvasive measurement in the upper airway obstruction to measure the outcomes of balloon dilatation.[9]

Treatment / Management

There are 3 main surgical approaches for subglottic stenosis, including endoscopic, open neck surgery, and tracheotomy. Endoscopic techniques include dilation either by balloon or rigid dilation. It also includes radical incision using a carbon dioxide laser and scar excision using a cold knife, without dilation. Finally, it often involves stent placement, as well. Adjunctive therapies for endoscopic surgery also include topical mitomycin and glucocorticoid injection. Mitomycin has antifibrogenic and antineoplastic activity. The goal of these approaches is to improve the patency of the airway in the long term and avoid dyspnea symptoms.[10] 

Patients with idiopathic subglottic stenosis are mostly managed endoscopically, and inter-dilation intervals may be increased with corticosteroid injection.[11] In pregnant women, the first-line treatment is the safest and most efficacious treatment for idiopathic subglottis stenosis. This treatment allows laryngeal dilation with the use of the continuous radial expansion of pulmonary balloons using noninvasive ventilation.[12] Balloon dilation may be considered as a first-line treatment for acquired subglottic stenosis. The success rate is highly related to the recently acquired stenosis, the initial grade of stenosis, younger patient age, and the absence of tracheotomy.[13] 

Mature and severe laryngeal stenosis in pediatric patients can also be treated successfully in patients with balloon dilation. In most severe cases with a prior tracheotomy, stenting is a must. Balloon dilation with stenting can also facilitate laryngotracheal reconstruction.[14] Also, endoscopic dilation is ideal due to being non-invasive; it is challenging to manage subglottic stenosis this way due to visual limitations and laser fire risk. Radiofrequency coblation has been used successfully for the resection of subglottic stenosis. Coblation has advantages, including rapid and precise coblation, little thermal damage, and safer and more convenient under direct visualization. It requires only a single operation that could simplify the tedious process of repeated ablation and reduce patient burden.[15] 

In an infant born with subglottic stenosis, traditional management is to do tracheostomy and access the child’s airway every 3 months to decide for the need for reconstructive surgery. The second option is to perform anterior or posterior cricoid split under general anesthesia to enlarge the cricoid lumen. The optimal treatment for acquired subglottic stenosis is laryngotracheal reconstruction. In laryngotracheal reconstruction, a separate incision above the tracheostomy at the level of cricoid is made, and the larynx is exposed from the hyoid above to the tracheostomy below. The lumen is entered above the superior thyroid notch, and the larynx is incised strictly in the midline. The graft is taken from costal cartilage and inserted to widen the cricoid ring. A silastic stent is used to prevent the collapse of the graft. During the closure of the incision, it is very important to oppose the anterior commissure accurately.[16]

Differential Diagnosis

Tracheal and laryngeal pathologies can be categorized into stenosis, infection, neoplasm, and aspiration.[17] Airway stenosis, more specifically, has been found to be caused by subglottic stenosis, tracheal stenosis, vascular ring, aberrant innominate artery, and laryngeal web.[18] From this list, tracheal stenosis can commonly be caused by prolonged intubation, surgery, disorders (autoimmune and inflammatory), infection, and GERD.[19] 

The differential diagnosis for subglottic stenosis, more specifically, can be benign or malignant. Benign causes include diseases like posttraumatic status, infection and rheumatic disease, and tumors like papilloma, hemangioma, and granular cell tumor. Malignant differentials include squamous cell carcinoma, chondrosarcoma, and laryngeal lymphoma.[20]

Staging

The most common grading for the diagnosis of subglottic stenosis is the Meyer-Cotton grading scale.

  • Grade 1 stenosis is lumen obstruction less than 50%.
  • Grade 2 stenosis is lumen obstruction between 51% and 70%.
  • Grade 3 stenosis is lumen obstruction between 71% and 99%.
  • Grade 4 stenosis is complete lumen obstruction.

Prognosis

Symptomatically, subglottic stenosis improves after endoscopic dilation, but the prognosis is not good as recurrence rates remain high.[21] Endoscopic management can be useful for subglottic stenosis, either for initial treatment or as adjunctive therapy (for example, in restenosis). However, a lower grade of initial subglottic stenosis suggests a higher grade of success with minimally invasive procedures.[22]

Complications

Subglottic stenosis may require surgery, and while endoscopic management is often preferred, open reconstruction is better in the cases of more severe stenosis. Tracheostomy, on the other hand, poses multiple complications, and this management option should be avoided if possible.[17] 

One study shows that restenosis was an observed complication in approximately a quarter of those patients who received endoscopic or surgical treatment. Revision surgery was also a complication, primarily due to either re-stenosis or peristomial tracheomalacia. Finally, tracheostomy tube insertion also posed a risk of mucosal obstruction.[23] The surgical prognosis can be excellent and complications minimized if care is taken to avoid anastomotic tension and devascularization.[2]

Consultations

Otolaryngology consultation is beneficial in managing upper airway obstruction, including subglottic stenosis.

Deterrence and Patient Education

It is important to identify common risk factors for subglottic stenosis to prevent the occurrence or minimize the severity. Such factors include GERD, autoimmune and inflammatory disorders, infection, and even surgical procedures and prolonged intubation.[19] As these are common causes of stenosis, they should be avoided or, if inevitable, promptly treated. If surgery is necessary, endoscopic management is preferred. Open surgery should be reserved for only severe cases, and tracheostomy should be avoided altogether, if possible.

Enhancing Healthcare Team Outcomes

Healthcare providers must make sure that patients are in good health, including but not limited to the presenting complaint. One article focuses on the importance of interprofessional team approach and the associated 6 C’s standing for care, communication, courage, compassion, commitment, and competence.[24] 

The results are further reinforced by a large-scale randomized control trial that shows the effectiveness of collaboration in critical care. It shows that a collaborative model for critical care in acute respiratory failure patients will prove useful in improving recovery. For example, in subglottic stenosis, an interprofessional team should involve an otolaryngologist, an intensivist, an anesthesiologist, and a pulmonologist to optimize patient care. [Level 1][25]


Article Details

Article Author

Nitish Jagpal

Article Editor:

Nadeem Shabbir

Updated:

10/12/2020 9:54:39 PM

PubMed Link:

Subglottic Stenosis

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