Subglottic stenosis (SGS) is a narrowing of the subglottic airway, which is housed in the cricoid cartilage. The image below shows an intraoperative endoscopic view of a normal subglottis.
The subglottic airway is the narrowest area of the airway, since it is a complete, nonexpandable, and nonpliable ring, unlike the trachea, which has a posterior membranous section, and the larynx, which has a posterior muscular section. The term subglottic stenosis (SGS) implies a narrowing that is created or acquired, although the term is applied to both congenital lesions of the cricoid ring and acquired subglottic stenosis (SGS). See the images below.
History of the Procedure
Early in the 20th century, acquired subglottic stenosis (SGS) was usually related to trauma or infection from syphilis, tuberculosis, typhoid fever, or diphtheria. Also, children often had tracheotomies placed that caused laryngeal stenosis. In this era, attempted laryngeal dilation failed as a treatment for subglottic stenosis (SGS).
Acquired subglottic stenosis (SGS) occurred increasingly in the late 1960s through the 1970s, after McDonald and Stocks (in 1965) introduced long-term intubation as a treatment method for neonates in need of prolonged ventilation for airway support. The increased incidence of subglottic stenosis (SGS) focused new attention on the pediatric larynx, and airway reconstruction and expansion techniques were developed. [1, 2, 3]
Surgery without cartilage expansion
In 1971, Rethi and Rhan described a procedure for vertical division of the posterior lamina of the cricoid cartilage with Aboulker stent placement. A metal tracheotomy tube was attached to the Aboulker stent with wires, and the anterior cartilaginous incision was closed. In 1974, Evanston and Todd described success with a castellated incision of the anterior cricoid cartilage and upper trachea, which was sewn open, and a stent made of a rolled silicone sheet was placed in it for 6 weeks. In 1980, Cotton and Seid described a procedure, in which tracheotomy is avoided, called the anterior cricoid split (ACS). The procedure was designed for use in neonates (usually, those born prematurely) with anterior glottic stenosis or SGS who had airway distress after extubation. The cricoid ring was divided anteriorly and a laryngofissure was created in an attempt to expand the airway without a tracheotomy. Holinger et al also described success with this procedure in 1987.
Surgery with cartilage-grafting reconstruction
In 1974, Fearon and Cotton described the successful use of cartilage grafts to enlarge the subglottic lumen in African green monkeys and in children with severe laryngotracheal stenosis.  All augmentation materials were evaluated, including thyroid cartilage, septal cartilage, auricular cartilage, costal cartilage, hyoid bone, and sternocleidomastoid myocutaneous flaps. After significant work, it appeared that costal cartilage grafts had the highest success rate.
In the 1980s, Cotton reported his experience with laryngeal expansion with cartilage grafting. His success rates depended on degree of stenosis: More severe forms of stenosis required multiple surgical procedures. Cotton used the Aboulker stent.
In 1991, Seid et al described a form of single-stage laryngotracheal reconstruction in which cartilage was placed anteriorly to expand the subglottis and upper trachea to avoid a tracheotomy. 
In 1992, Cotton et al described a 4-quadrant cricoid split, along with anterior and posterior grafting.  In 1993, Zalzal reported 90% decannulation with any degree of subglottic stenosis (SGS) with his first surgical procedure.  Zalzal customized the reconstruction on an individual basis, and most patients received Aboulker stents for stabilization.
In 1993, Monnier described partial cricotracheal resection with primary anastomoses for severe SGS, since grade III and grade IV SGS (ie, severe SGS) often requires multiple (3-4) surgical augmentations for decannulation. In 1997, Cotton described his experience with the procedure, reporting a decannulation rate higher than 90% for primary and rescue cricotracheal resection.
Subglottic stenosis (SGS) is narrowing of the subglottic lumen. Subglottic stenosis (SGS) can be acquired or congenital. Acquired subglottic stenosis (SGS) is caused by either infection or trauma, as seen in the images below. Congenital subglottic stenosis (SGS) has several abnormal shapes.
Holinger evaluated 29 pathological specimens obtained in children with congenital cricoid anomalies. Half of these children had an elliptical cricoid cartilage, as shown below, which Tucker first described in 1979.
Elliptical cricoid cartilage was the most commonly observed congenital abnormality. Other observed abnormalities included a flattened anterior shape, a thickened anterior cricoid, and a submucosal posterior laryngeal cleft.
The frequency of congenital subglottic stenosis (SGS) is unknown.
The incidence of acquired subglottic stenosis (SGS) has greatly decreased over the past 40 years. In the late 1960s, when endotracheal intubation and long-term ventilation for premature infants began, the incidence of acquired subglottic stenosis (SGS) was as high as 24% in patients requiring such care. In the 1970s and 1980s, estimates of the incidence of subglottic stenosis (SGS) were 1-8%.
In 1998, Choi reported that the incidence of subglottic stenosis (SGS) had remained constant at the Children's National Medical Center in Washington, DC; it was approximately 1-2% in children who had been treated in the neonatal ICU.  Walner recently reported that, among 504 neonates who were admitted to the level III ICU at the University of Chicago in 1997, 281 were intubated for an average of 11 days, and in no patient did subglottic stenosis (SGS) develop over a 3-year period. In 1996, a report from France also described no incidence of subglottic stenosis (SGS) in the neonatal population who underwent intubation with very small endotracheal tubes (ie, 2.5-mm internal diameter) in attempts to prevent trauma to the airway.
The cause of congenital subglottic stenosis (SGS) is in utero malformation of the cricoid cartilage.
The etiology of acquired subglottic stenosis (SGS) is related to trauma of the subglottic mucosa. Injury can be caused by infection or mechanical trauma, usually from endotracheal intubation but also from blunt, penetrating, or other trauma. Historically, acquired subglottic stenosis (SGS) has been related to infections such as tuberculosis and diphtheria.  Over the past 40 years, the condition has typically been related to mechanical trauma.
Factors implicated in the development of subglottic stenosis (SGS) include the size of the endotracheal tube relative to the child's larynx, the duration of intubation, the motion of the tube, and repeated intubations. Additional factors that affect wound healing include systemic illness, malnutrition, anemia, and hypoxia. Local bacterial infection may play an important roll in the development of subglottic stenosis (SGS). Gastroesophageal reflux (GER) may play an adjuvant role in the development of subglottic stenosis (SGS) because it causes the subglottis to be continually bathed in acid, which irritates and inflames the area and prevents it from healing correctly. A systemic or gastrointestinal allergy may cause the airway to be more reactive, creating a greater chance of developing stenosis.
Acquired subglottic stenosis (SGS) is often caused by endotracheal intubation. Mechanical trauma from an endotracheal tube, as it passes through or remains for long periods in the narrowed neonatal and subglottic airway, can lead to mucosal edema and hyperemia. These conditions then can progress to pressure necrosis of the mucosa. These changes have been observed within a few hours of intubation and may progress to expose the perichondrium of the cricoid cartilage. Infection of the perichondrium can result in a subglottic scar. This series of events can be hastened if an oversized endotracheal tube is used. Always check for an air leak after placing an endotracheal tube because of the risk of necrosis of the mucosa, even in short surgical procedures. This practice is common among anesthesiologists. Usually, the pressure of the air leak should be less than 20 cm of water, so that no additional pressure necrosis occurs in the mucosa of the subglottis.
Children with subglottic stenosis (SGS) have an airway obstruction that may manifest in several ways. In neonates, subglottic stenosis (SGS) may manifest as stridor and obstructive breathing after extubation that requires reintubation. At birth, intubation in most full-term neonates should be performed with a 3.5-mm pediatric endotracheal tube. If a smaller-than-appropriate endotracheal tube must be used, narrowing of the airway may be present, which could suggest subglottic stenosis (SGS).
The stridor in subglottic stenosis (SGS) is usually biphasic. Biphasic stridor can be associated with glottic, subglottic, and upper tracheal lesions. Inspiratory stridor usually is associated with supraglottic lesions; expiratory stridor usually is associated with tracheal, bronchial, or pulmonary lesions.
The level of airway obstruction varies depending on the type or degree of subglottic stenosis (SGS). In mild subglottic stenosis (SGS), only exercise-induced stridor or obstruction may be present. In severe subglottic stenosis (SGS), complete airway obstruction may be present and may require immediate surgical intervention.
Depending on the severity, subglottic stenosis (SGS) can cause patients to have decreased subglottic pressure and a hoarse or a weak voice. Hoarseness or vocal weakness also can be associated with glottic stenosis and vocal cord paresis or paralysis.
Always ask about a history of recurrent croup. A child with an otherwise adequate but marginal airway can become symptomatic with the development of mucosal edema associated with a routine viral upper respiratory infection (URI). Children with these conditions may have subglottic narrowing and an evaluation of the airway is appropriate.
Always assess the history of GER disease (GERD). If present, always evaluate GERD prior to surgical intervention. A child who eventually has a diagnosis of subglottic stenosis (SGS) often has a history of either laryngotracheal trauma or intubation and ventilation. Frequently, these patients were born prematurely, have bronchopulmonary dysplasia, and may require oxygen administration. The degree of pulmonary disease and the amount of oxygen the child requires may affect the ability to perform decannulation. Prior to surgical intervention, the child should not require a substantial oxygen supplementation.
The physical examination varies depending on the degree of subglottic stenosis (SGS) present. Auscultate the child's lung fields and neck to assess any symptoms of airway obstruction and to evaluate pulmonary function. Completely evaluate the head and neck, and identify associated facial abnormalities such as cleft palate, choanal atresia, retrognathia, and facial deformities. Evaluate the child's initial overall appearance, and ask the following questions:
Is the child comfortable?
Does the child have difficulty breathing?
Does the child have difficulty breathing when emotionally upset?
Does the child have any suprasternal, substernal, or intercostal retractions?
Does the child have any nasal flaring?
Is the voice normal? Is it weak? Is the voice breathy?
Does the child have stridor? If so, what is the nature of the stridor (ie, inspiratory, expiratory, or biphasic)?
What is the child's neurologic status?
Does the child have a tracheotomy? Can the patient occlude the tracheotomy and still breathe without laboring?
Surgical reconstruction is performed on the basis of the symptoms, regardless of SGS grade. Children with grade I and mild grade II subglottic stenosis (SGS) often do not require surgical intervention.
Myers and Cotton devised a classification scheme for grading circumferential subglottic stenosis from I-IV, which is established endoscopically and by using noncuffed pediatric endotracheal tubes of various sizes and sizing the airway. The scale describes stenosis as a percent of area that is obstructed.
The system contains 4 grades, as follows:
Grade I - Obstruction of 0-50% of the lumen obstruction
Grade II - Obstruction of 51-70% of the lumen
Grade III - Obstruction of 71-99% of the lumen
Grade IV - Obstruction of 100% of the lumen (ie, no detectable lumen)
The percentage of stenosis is evaluated by using endotracheal tubes of different sizes. The largest endotracheal tube that can be placed with an air leak less than 20 cm of water pressure is recorded and evaluated against a scale that has previously been constructed by Myers and Cotton, as depicted below.
This grading system applies mainly to circumferential stenosis and does not apply to other types of subglottic stenosis (SGS) or combined stenoses, although it can be used to obtain a rough estimate. Typically, children with grade I, as shown in the image below, or mild grade II stenosis do not require surgical intervention. Children with these conditions may have intermittent airway symptoms, especially when infection or inflammation causes mucosal edema.
Surgical intervention may be avoided if periods of airway obstruction are rare and can be treated on an inpatient or outpatient basis with anti-inflammatory and vasoconstrictive agents, such as oral, intravenous, or inhaled steroids and inhaled epinephrine (racemic treatment). If children with these conditions continue to have intermittent or persistent stridor and airway obstructive symptoms when they are well, or if they frequently become ill, surgical intervention may be necessary.
Development of upper respiratory symptoms during routine infections can indicate whether a child with subglottic stenosis (SGS) requires surgical reconstruction. Viral infections of the upper respiratory tract can create swelling in any area of the respiratory epithelium from the tip of the nose to the lungs. If a child with subglottic stenosis (SGS) has a cold and/or bronchitis but no significant symptoms of stridor or upper airway obstruction, the airway may be large enough to tolerate stress, and reconstruction may not be needed. A history of recurrent croup suggests subglottic stenosis (SGS).
Occasionally, older children have exercised-induced airway obstruction. At evaluation, these children may have grade I or grade II subglottic stenosis (SGS). Expansion of the airway with cartilage augmentation may allow them to lead a healthy and active lifestyle.
Children with grade III or grade IV subglottic stenosis (SGS) need one or more of the forms of surgical treatment discussed in Surgical therapy.
Although croup, bacterial infection, GERD, and bronchopulmonary dysplasia may occur or be involved in the development of subglottic stenosis (SGS), a history of prolonged endotracheal tube intubation is the most common factor seen in patients with subglottic stenosis (SGS) that requires surgical correction.
The subglottis is defined as the area of the larynx housed by the cricoid cartilage that extends from 5 mm beneath the true vocal cords to the inferior aspect of the cricoid ring, depicted in the image below. Because of the proximity and close relationship of the subglottis to the glottic larynx, glottic stenosis often can be present with subglottic stenosis (SGS). When SGS is corrected surgically, good voice quality can be preserved by not violating the true vocal cords if they are uninvolved in the disease process.
When creating the entry incision into the airway in an isolated subglottic stenosis (SGS), divide the cricoid cartilage, upper 2 tracheal rings, and the inferior third to half of the laryngeal cartilage in the midline; avoid dividing the anterior commissure. However, if the disease dictates or if exposure for repair cannot be obtained without dividing the anterior commissure, carefully perform the procedure. Endoscopic guidance can help in preventing injury to the glottic larynx.
If a laryngofissure is required for glottic stenosis or to gain access to the posterior aspect of the stenosis for suturing of the posterior graft, care must be taken to identify the anterior commissure and correctly put it back into place. Once the laryngofissure is created in the midline, immediately suture the anterior aspect of the true vocal chords near the anterior commissure to the laryngeal cartilage with a 6-0 monofilament suture such as polydioxanone (PDS) or Monocryl. This procedure helps prevent anterior commissure from becoming blunted and helps mark approximately where it should be once the laryngofissure is closed.
When dividing the posterior cricoid lumen, note that the esophagus is immediately adjacent and posterior to it. Take care to avoid injuring the esophagus when completely dividing the posterior cricoid lamina during cartilage augmentation.
The recurrent laryngeal nerves enter the larynx in the posterior lateral portion of the cricoid ring. When surgery is performed in the midline, the recurrent laryngeal nerves should be far enough away from an anterior division to prevent injury. Any surgical procedure in which the lateral cricoid is divided could jeopardize the laryngeal nerve and result in paresis or paralysis of the true vocal cords. In the cricotracheal resection procedure, no attempt is made to identify the recurrent laryngeal nerves because of dense scarring. This lack of identification has resulted in some reported cases of paresis of the true vocal cord.
No specific absolute contraindications to the laryngotracheal reconstruction procedure exist. However, if general anesthesia is absolutely contraindicated, surgical correction of subglottic stenosis (SGS) cannot be performed.
A relative contraindication to reconstruction of a narrow subglottis is present in children who have a tracheotomy and subglottic stenosis (SGS) but need a tracheotomy for other purposes (eg, access for suctioning secretions caused by chronic aspiration) or in those who have airway collapse or obstruction in the nasal cavity, nasopharynx, oral cavity, oropharynx, supraglottic larynx, or trachea that cannot be repaired. However, if severe or complete laryngeal obstruction exists and if the child might be able to vocalize if the airway were surgically corrected, reconstruction may be beneficial, despite the need to maintain the tracheotomy tube. Severe GER is another relative contraindication. Once GER is treated successfully (medically or surgically) or resolves on its own, reconstruction can be considered. An additional relative contraindication to airway reconstruction is pulmonary or neurological function that is inadequate to withstand tracheotomy decannulation.
Regardless of the cause of subglottic stenosis (SGS), it is usually best to delay reconstructive efforts in children who have reactive or granular airways, shown below, until the reactive nature of the patient's condition subsides.
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