What Region Is Subglottis?
The subglottis region is the lower part of the larynx (voice box) located below the vocal cords and leads to the trachea (windpipe). It is the narrowest part of the airway in children. It is cylindrical and enlarges in diameter as it progresses downwards
What Is Subglottic Stenosis?
Subglottic stenosis is the narrowing of the airway below the level of vocal cords and until the trachea. The normal subglottic diameter of a newborn is 4 mm. When it narrows down below 3.5 mm, the condition is referred to as subglottic stenosis. Though it most commonly occurs in newborns, acquired type of subglottic stenosis occurs in adults too. Scarring of the larynx below the vocal cords causes the narrowing. This can, at times, involve the vocal cords and affect the voice.
What Are the Types and Causes of Subglottic Stenosis?
Subglottic stenosis is of two types based on their etiology;
Congenital Subglottic Stenosis -
In this type, the baby is born with a narrow airway. This is a rare birth defect that the baby is born with and is usually associated with other syndromes and genetic conditions. The airway cartilage of the baby is not developed properly before birth resulting in narrow airways.
Acquired Subglottic Stenosis -
As the name indicates, this type is acquired after birth at any point in life due to etiologies such as:
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Prolonged Endotracheal Intubation - In neonates with respiratory problems, long-term intubation for airway support was introduced as the treatment method by McDonald and Stocks in 1965. This greatly increased the incidence of subglottic stenosis in that era.
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Burns.
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Ingestions.
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Infections - Syphilis, tuberculosis, diphtheria, and typhoid fever.
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Inflammation - Wegener’s granulomatosis, gastroesophageal reflux disease (GERD).
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Trauma - External trauma due to road traffic accidents, clothesline injuries, and internal trauma due to iatrogenic causes like endotracheal intubation are the chief causes of acquired subglottic stenosis.
Why Is Intubation an Important Cause of Subglottic Stenosis?
The acquired type is more common compared to the congenital type, and endotracheal intubation remains to be the chief cause among the etiologies.
After 17 hours of intubation in adults and one week in newborns, acquired subglottic stenosis can occur. This extended period of tolerance to intubation in infants is due to the flexible cartilage, funnel-shaped larynx, its location at a higher level, and posterior tilt.
During intubation in full-term newborns, a 3.5 mm tube must be used. If a condition arises necessitating the use of smaller endotracheal tubes, a narrowed subglottic must be suspected.
The following factors are implicated in the development of subglottic stenosis:
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Size of the endotracheal tube compared to the child’s laryngeal lumen size.
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Endotracheal tube cuff pressure and duration of inflation of the cuff.
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Duration of intubation.
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Movements of the tube.
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The number of repeated intubations.
In addition to injury due to intubation, poor wound healing due to the following factors also play a crucial role:
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Malnutrition.
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Hypoxia.
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Any systemic illness.
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Allergy (systemic or gastrointestinal).
What Is the Pathophysiology of Acquired Subglottic Stenosis?
Endotracheal intubations cause mechanical trauma to the narrowed subglottis when they pass through it or remain for more extended periods. As a result, edema of the inner lining of the subglottis and hyperemia occurs. The prolonged pressure it exerts on the narrowed subglottis leads to pressure necrosis of the inner lining. Furthermore, infection and subsequent subglottic scar formation occur.
How Is Subglottic Stenosis Graded?
To measure the severity of the condition, the below grading system is used:
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Grade 1 (0 to 50 % narrowing) - There are no symptoms.
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Grade 2 (50 to 70 % narrowing) - Mild breathing difficulty with strenuous physical activity will be present.
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Grade 3 (70 to 99 % narrowing).
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Grade 4 (Complete obstruction).
Symptoms of grades 3 and 4 are so severe that the affected individuals would require a tracheostomy to survive before getting treated for stenosis.
How Common Is Subglottic Stenosis?
This is an uncommon condition with an incidence of 2 % and below. This rare condition is more common in newborns and children than in adults. Endotracheal intubation, though a necessary and unavoidable procedure in individuals needing to secure their airway, is itself the most common culprit in subglottic stenosis. Hence appropriate tubes must be used. Tubes with an inner diameter not exceeding 7 mm to 8 mm in adult males and 6 mm to 7 mm in adult females are advised.
What Signs and Symptoms Does Subglottic Stenosis Cause?
Those with subglottic stenosis have airway obstruction. This airway obstruction can be manifested as:
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Stridor (an abnormal and high-pitched sound produced from the airways due to partial blockage).
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Obstructive breathing following extubation.
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Hoarse voice.
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Increased effort to breathe.
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Multiple episodes of croup in children.
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Difficulty gaining weight.
In mild subglottic stenosis cases, there is obstructive breathing following exercise or physical exertion only. But in severe subglottic stenosis, obstructive breathing is so worse that immediate surgical intervention is required to save a life.
What Tests and Investigations Help Confirm Subglottic Stenosis?
In the case of infants, a detailed medical history regarding prematurity, intubation duration, birth weight, lung diseases, etc., will be taken. This remains imperative in diagnosis. Furthermore, the following tests will be ordered:
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Neck X-Rays - These reveal masses in the subglottic region or its narrowing.
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Endoscopy with micro laryngoscopy and bronchoscopy.
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CT (computed tomography) scan of the chest.
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Airway fluoroscopy.
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Barium-enhanced esophagram to rule out GERD (gastroesophageal reflux disease) because children with subglottic stenosis have a three-fold increased risk of having GERD.
How Is Subglottic Stenosis Treated?
Based on the severity of stenosis, the treatment also varies.
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Mild Subglottic Stenosis - In mild cases, conservative and supportive management is advised. Neonates with minimal to no symptoms and mild stenosis eventually get better with growth. Careful observation of the child is of utmost importance as they are more likely to get breathing problems with common respiratory diseases like cold, flu, etc.
In some instances, balloon dilation of the subglottis will also be done. The scar tissues causing narrowing are removed with lasers and microdebriders.
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Severe Subglottic Stenosis - Children and adults with severe stenosis require a tracheostomy tube to survive, without which they would not be able to breathe. Subglottic stenosis repair with open laryngotracheal reconstruction surgery or partial cricotracheal resection is employed to remove the scar tissues and expand the airway.
What Is the Prognosis of Acquired Subglottic Stenosis?
Based on the grade of stenosis and treatment method, success rates vary. Around 80 % to 90 % success rates were reported with surgical intervention. The presence of GERD, respiratory illnesses, reactive larynx, and age factors (children younger than two years of age) affect the prognosis.
Conclusion:
In the absence of a history of intubation and other acquired causes, subglottic stenosis is mostly congenital even in adults. Adults without acquired subglottic stenosis have undiagnosed congenital stenosis, which would have been misdiagnosed as asthma or other respiratory condition. Hence, difficulty in breathing should not be ignored or mistaken for asthma in children and adults. Immediate medical help must be sought.
