Anatomy & Pathophysiology:
Stridor is a symptom, not a diagnosis or disease; it is the sound generated by turbulent airflow through the partially obstructed upper airway. Stridor should be distinguished from stertor, which refers to a coarse, snoring sound produced as a result of nasopharyngeal or oropharyngeal obstruction. Poiseuille's Law dictates that airway resistance is inversely proportional to the fourth power of the radius; therefore, additional narrowing of the pediatric airway will result in a significant and sometimes dramatic increase in resistance, manifested as stridor. The presentation of stridor in a child can be classified in multiple ways: by the acuteness or chronicity of its onset, the phase of stridor in the respiratory cycle, the character of the sound, the age of the child, associated symptoms, and association with other congenital anomalies. The timing provides clues as to the location of the obstruction. Inspiratory stridor suggests a supraglottic or glottic etiology, expiratory stridor is typically due to a tracheal or bronchial obstruction, and biphasic stridor indicates subglottic pathology (where the fixed obstruction is not affected by laryngeal or tracheal dynamics).
There are many causes of upper airway obstruction in infants and children; these include congenital malformations, infectious or inflammatory swelling, trauma (particularly foreign body aspiration), and neoplastic compression of the airway. The most common cause of stridor in children is laryngomalacia, a congenital abnormality of the supraglottis (the portion of the larynx above the vocal cords), wherein the excessively curled ("omega-shaped") immature epiglottis prolapses onto the vocal cords with negative pressure on inspiration. Gastroesophageal reflux is thought to contribute to worsening airway obstruction from inflammation and edema in laryngeal tissues.
Congenital or acquired vocal cord paralysis is a glottic cause of pediatric stridor. The severity of symptoms depends on whether the paralysis is unilateral or bilateral, as well as the position in which the cords are paralyzed and, in unilateral cases, how well the mobile cord is able to compensate. Congenital vocal cord paralysis is rare; it is generally related to central nervous system disease, such as the Arnold-Chiari malformation. Acquired vocal cord paralysis is typically seen as a result of injury to the recurrent laryngeal nerve during congenital cardiac surgery.
Recurrent respiratory papillomatosis (RRP) is another condition that frequently involves the glottis, although papillomas may be found anywhere in the larynx and tracheobronchial tree. The disease is caused by human papillomavirus infection (particularly HPV strains 6 and 11). In children, transmission is thought to occur during vaginal delivery; the new quadrivalent HPV vaccine prevents vaginal infection and is therefore protective against RRP in offspring of immunized females.
The subglottis (area below the vocal cords) is the narrowest segment of the pediatric airway. Consequently it is particularly vulnerable to obstruction due to infection and intubation trauma. Laryngotracheobronchitis (also known as croup), a viral infection of the trachea and larynx, is the most common cause of stridor in children between 1-3 years of age. Acquired subglottic stenosis is most commonly a result of prolonged endotracheal intubation, causing inflammation and eventual scar formation in the subglottis. The subglottis is also the most common site for laryngeal hemangiomas, which are benign vascular growths. Subglottic hemangiomas may be isolated or, in 50% of cases, they may be associated with cutaneous hemangiomas or vascular syndromes.
Finally, infectious diseases such as epiglottitis, and bacterial tracheitis should also be considered as causes of pediatric stridor. These conditions generally present with additional respiratory or systemic symptoms and are not discussed in detail in this text.
The prevalence and incidence of laryngomalacia are unknown, although it is the most common cause of pediatric stridor and the most common congenital laryngeal abnormality. It is primarily diagnosed in the first few weeks or months of life, with peak presentation around 6 to 9 months of age.
Vocal cord palsy is the second most common congenital laryngeal abnormality, but is considered rare. Likewise, laryngeal cysts, posterior laryngeal clefts, and congenital subglottic stenosis are also rare anomalies.
Subglottic hemangioma is more common in females and typically presents by 6 months of age. In 50% of cases, it is associated with cutaneous hemangioma. Facial cutaneous hemangiomas that occur in a beard-like distribution are associated with concurrent subglottic hemangioma in 63% of cases.
Respiratory papillomatosis is the most common pediatric laryngeal neoplasm. There is no sex predilection, and it is generally diagnosed between the ages of 2 and 5 years. There is an association between a history of maternal genital warts and development of disease.
The natural history of pediatric stridor depends on the etiology. Laryngomalacia self-resolves in the majority of cases by 18 months of age without treatment; about 10% of patients with laryngomalacia require surgical intervention. Likewise, hemangiomas typically begin to involute starting at 12 months of age, with complete resolution by 5 years, although many patients will require intervention during the initial proliferative phase. If observed, some other causes of airway obstruction may produce fewer symptoms with age, as the airway enlarges. Respiratory papillomatosis has a tendency to recur, sometimes after long periods of remission. Hoarseness is the primary symptom; however, when it progresses to stridor, airway compromise is imminent.
A stridorous child may present in varying degrees of respiratory distress, depending on the severity of obstruction. The child may exhibit tachypnea, dyspnea, or increased work of breathing, with suprasternal or intercostal retractions, nasal flaring, or accessory muscle use. Apneic or cyanotic episodes may also be reported. In some cases, stridor may be heard continuously, while in others, it may manifest only with sleep, feeding, agitation, or in certain positions.
Aspiration may be observed, particularly in cases of glottic abnormality (such as vocal cord paralysis or posterior laryngeal cleft). If airway obstruction interferes sufficiently with feeding, the child may exhibit failure to thrive. Other long term sequelae of chronic airway obstruction include pulmonary hypertension and cor pulmonale, as is seen with sleep disordered breathing.
The mnemonic "SPECS-R" is a useful guide when taking the history of a child with stridor:
Severity – assess acuity and degree of respiratory distress, including exacerbating or alleviating factors
Progression – assess whether symptoms are improving, stable, or deteriorating
Eating – assess for symptoms such as aspiration and failure to thrive
Cyanosis – assess for episodes of cyanosis or apnea, which suggest a more severe disease process
Sleep – assess for apneic episodes and other sleep disturbances, which may result in long term sequelae
Radiology – determine whether radiographic studies are available, which may be useful for diagnosing anatomic anomalies
Differential Diagnosis of Pediatric Stridor:
- Vallecular cyst
- Laryngeal cyst
- Laryngeal web
- Posterior laryngeal cleft
- Vocal cord palsy (e.g., due to neurologic condition)
- Hemangioma (may also be found outside of subglottis)
- Subglottic stenosis
- Tracheal stenosis/complete tracheal rings
- Compression due to vascular anomaly
- Mass effect due to tumor or cyst
- Vocal cord palsy (e.g., idiopathic)
- Subglottic stenosis (e.g., intubation trauma)
- Respiratory papillomatosis
- Inflammatory disease (e.g., croup, epiglottitis)
- Foreign body
- Thermal or caustic injury
- Laryngeal trauma (e.g., fracture)
- Inflammatory disease (e.g., bacterial tracheitis)
- Foreign body
- Mass effect due to tumor, cyst, or abscess
The proper management of a stridorous child requires an immediate judgment of the degree of airway obstruction as evidenced by the acuity and harshness of the symptoms. When there is severe respiratory distress, intervention may preempt a thorough evaluation. On the other hand, when the symptoms are more moderate, there is time to assess the context and history of the patient, perform a physical evaluation including visualization of the airway, and obtain ancillary diagnostic services in order to make a diagnosis.
Any witnessed choking episodes or suspicion for foreign object ingestion or inhalation should be noted. The history should also document whether there was any neonatal respiratory distress or any prior intubations. If so, the duration of intubation and number of attempts necessary to extubate should be elicited.
In a stable child, a complete examination includes the phase of stridor, signs of increased work of breathing, growth chart percentile trends, and evidence of any prior cervical or thoracic surgical procedures. The child may also be observed while feeding and when crying, particularly if the parents report exacerbation of symptoms with these activities. Change in voice quality may suggest a glottic etiology, such as vocal cord palsy or laryngeal papillomatosis. The neck should be palpated for masses that may be causing extrinsic compression of the larynx. The presence of cutaneous hemangiomas, particularly in a beard distribution, may be an indicator of subglottic hemangioma.
Laryngoscopy can provide a definitive diagnosis of the cause of stridor in many cases. Flexible fiberoptic laryngoscopy (FFL) may be performed in the office setting in a stable, cooperative patient. Although it does not provide as thorough an evaluation as direct laryngoscopy (for example, the subglottis is difficult to visualize), FFL is effective for diagnosing laryngomalacia and vocal cord palsy. It should be noted that, if epiglottitis is suspected based on history and clinical presentation, laryngoscopy should only be undertaken after first securing the airway. Any trauma to the larynx during manipulation may incite further edema and deterioration of an already tenuous airway.
In cases of laryngomalacia, the laryngoscopic findings may include an omega-shaped epiglottis, redundant arytenoid mucosa, foreshortened aryepiglottic folds, or supraglottic mucosal edema. The epiglottis may be seen to prolapse into the laryngeal inlet during inspiration.
Laryngeal masses and subglottic stenosis, as well as any tracheal or bronchial pathologies, are best evaluated with direct laryngoscopy and bronchoscopy, which must be performed in the operating room under general anesthesia. Direct laryngoscopy also allows for more accurate estimation of airway size. In cases of subglottic stenosis, the degree of obstruction is scored using the Myer-Cotton grading system. Details regarding direct laryngoscopy are provided in Direct Laryngoscopy with Bronchoscopy.
In certain cases, radiologic studies may be useful, particularly if there is concern for extralaryngeal masses or vascular anomalies. However, dynamic conditions such as laryngomalacia and vocal cord palsy cannot be diagnosed by radiology, and present imaging modalities lack the resolution to detect many laryngeal conditions, such as laryngeal webs or clefts.
Treatment options for pediatric stridor depend on the severity of respiratory distress and airway obstruction, as well as the etiology. Acute respiratory compromise may necessitate emergent intervention, such as intubation or tracheotomy, in order to secure the airway. Because of the morbidity associated with emergent pediatric tracheotomy, intubation is preferred in most acute circumstances. However, in cases of chronic obstruction, or if respiratory toilet is anticipated, a well done tracheotomy can be lifesaving.
Infectious causes of stridor are generally treated medically. Laryngotracheobronchitis is treated with steroids and supportive care (such as humidification). Severe cases may also benefit from administration of racemic epinephrine. Bacterial infections such as epiglottitis and bacterial tracheitis should be treated with respiratory support and the appropriate antibiotic regimen.
Most cases of laryngomalacia are mild and may be observed. Because of the relationship between laryngomalacia and laryngopharyngeal reflux, antireflux therapy should be initiated. Surgical treatment of laryngomalacia should be considered if the patient has cyanotic or apneic episodes, failure to thrive, or cardiopulmonary sequelae. Surgical methods of correcting laryngomalacia are collectively referred to as supraglottoplasty. Typically, this involves reduction of redundant tissue and/or release of shortened aryepiglottic folds using the CO2 laser. See Supraglottoplasty for details regarding this procedure.
Mild subglottic stenosis may be observed. Surgical options for more severe cases of subglottic stenosis include balloon dilatation and laryngotracheal reconstruction. Balloon dilatation may be considered in cases of both evolving and fixed stenoses and is performed using endovascular-type inflatable balloons. The balloon is inserted into the airway to the location of the stenosis and then inflated to an appropriate setting, generally around 10 atmospheres of pressure. In laryngotracheal reconstruction, the laryngeal framework is augmented using cartilage grafts in order to increase airway diameter.
Symptomatic RRP may be palliated with laser or microdebrider debulking of papillomas. Many types of adjunctive medications have been tried for RRP; none work predictably and patients often require repeat procedures to keep their symptoms under control.
Subglottic hemangioma is now primarily treated medically using propranolol, which causes hemangioma regression and allows for avoidance of surgical intervention in many cases. Intralesional steroid injection and laser ablation may be considered as alternatives in the event of propranolol failure.
Complications, Prognosis & Follow-Up:
If left untreated, severe airway obstruction can result in cardiopulmonary sequelae, including cor pulmonale, as well as malnutrition or failure to thrive if ability to feed is impaired as well.
The prognosis for laryngomalacia is favorable. Supraglottoplasty has a high success rate with the majority of failures occurring in patients with additional comorbidities.
Subglottic stenosis treated with open laryngeal surgery has a high reported success rate (80-90%). Complications associated with laryngotracheal reconstruction include restenosis and poor voice quality.
Surgery for recurrent respiratory papillomatosis, while temporarily effective, is not curative. Patients may require repeat ablations as frequently as once every 2-4 weeks. However, the disease generally enters a quiescent state in adolescence or young adulthood. Complications of untreated papillomas include change in voice quality, laryngotracheal stenosis, and rare malignant conversion.
- Inspiratory stridor arises from supraglottic or glottic obstruction, biphasic stridor arises from subglottic obstruction and expiratory stridor from tracheal obstruction.
- Proper management requires an immediate judgment of the degree of airway obstruction based on the acuity of the symptoms; when there is severe respiratory distress, intervention may preempt a thorough evaluation.
- Laryngomalacia is the most common cause of pediatric stridor; it is a congenital supraglottic abnormality resulting in prolapse of tissue into the laryngeal inlet during inspiration. Most cases spontaneously resolve, but severe or persistent cases may be addressed surgically with supraglottoplasty.
- The subglottis is the narrowest portion of the pediatric airway; acquired subglottic stenosis is most commonly due to prolonged endotracheal intubation. Subglottic stenosis may be treated with balloon dilatation or laryngotracheal reconstruction.
- Subglottic hemangiomas are frequently associated with cutaneous hemangiomas. The first-line approach to treatment is with propranolol administration.
- Recurrent respiratory papillomatosis is caused by infection with human papillomavirus. Patients typically present with hoarseness; development of stridor indicates substantial airway compromise. While no curative therapy is available, surgical debulking can provide temporary relief of symptoms.