KEY POINTS
- 1.
Stridor is a sound caused by obstruction of the upper airway, usually from abnormalities within one or more of the subsites of the larynx (supraglottis, glottis, and subglottis) or in the trachea.
- 2.
Stridor is a physical sign and not a diagnosis. It can be characterized by its presence during inspiration or expiration (or both), by its pitch and loudness, and by its change with activity or position.
- 3.
Laryngomalacia is the most common cause of neonatal stridor, and most cases will improve over the first 12 to 18 months of life.
- 4.
The second most common cause of neonatal stridor is vocal cord paralysis, but it is the likely diagnosis when stridor is observed immediately after delivery.
- 5.
Subglottic stenosis presents with stridor and airway obstruction and can be either congenital or acquired from prior endotracheal intubation.
- 6.
Subglottic hemangiomas should be suspected when stridor develops in infants 1 to 2 months of age, especially when cutaneous hemangiomas are also seen.
Introduction
Stridor describes the sound caused by turbulent airflow within the large airways during respiration. Stridor is typically high-pitched, although the sound can vary with changes in shape and caliber of the airway and with respiratory effort. Stridor can be inspiratory, expiratory, or biphasic, and this quality can indicate the likely site of obstruction. Inspiratory stridor is associated with extrathoracic airway obstruction, typically at the level of the vocal cords or above. Expiratory stridor may be seen with intrathoracic obstruction within the middle or distal trachea. Biphasic stridor indicates obstruction at the level of the vocal cords, subglottis, or upper trachea and is characterized by noise during both inspiration and expiration, although the inspiratory component often predominates. Stridor must be differentiated from stertor: a low-pitched, gurgly, inspiratory or expiratory sound caused by reverberation of redundant soft-tissue or secretions within the oropharynx, nose, or nasopharynx. Stridor and stertor may coexist or be present in isolation.
Stridor in neonates is most commonly caused by laryngomalacia. The other likely causes of stridor in newborns are vocal cord paralysis and subglottic stenosis. Stridor may present immediately at birth or within days to months. Stridor is a sign, not a diagnosis, and persistent stridor in a neonate necessitates formal diagnostic evaluation. Although laryngomalacia, the most common cause of neonatal stridor, typically has a favorable course and requires little intervention, stridor may signal a potentially progressive airway lesion that mandates urgent action. However, with proper evaluation and management, most infants with neonatal stridor have a good prognosis.
Pathophysiology and Clinical Features
Stridor can emanate from obstruction at any level of the larger airways. It can be explained using the Bernoulli principle: when airway diameter decreases at the level of an obstruction, air flow velocity increases exponentially, resulting in negative pressure and airway collapse behind it. Therefore typical laminar flow is disrupted and the turbulent flow results, vibrating the surrounding upper airway soft tissues with resultant stridor.
The larynx has three subsites: the supraglottis, glottis, and subglottis ( Fig. 67.1 ). The supraglottis includes the cartilaginous structures above the true vocal cords, including the epiglottis and arytenoid cartilages and the false vocal folds. The glottis includes the true vocal cords. The subglottis is the area just below the true vocal cords and includes the cricoid cartilage. Stridor may also be a result of narrowing of the trachea, which is composed of C-shaped cartilaginous rings with a muscular membrane posteriorly.
Clinical features of a newborn with stridor often suggest the site of obstruction and likely pathology ( Table 67.1 ). A careful clinical assessment will allow appropriate timing and selection of diagnostic studies.
| Condition | Clinical Presentation | Symptom Onset, Severity, and Progression | Key Diagnostic Procedure and Additional Tests to Consider |
|---|---|---|---|
| Supraglottis | |||
| Laryngomalacia |
| Onset: first 2 weeks of life Severity: most commonly mild, but can be severe Progression: may initially worsen; typically resolved in 6–18 months | Fiberoptic laryngoscopy
|
| Cysts (saccular, ductal, vallecular) |
| Onset: at birth Severity: variable with size/location of mass Progression: stable | Fiberoptic laryngoscopy
|
| Glottis | |||
| Vocal cord paralysis |
| Onset: congenital paralysis manifests at birth; acquired paralysis may present after extubation or after neck/chest procedure Severity and progression: variable; many cases resolve over time | Fiberoptic laryngoscopy
|
| Glottic web |
| Onset: at birth Severity: variable Progression: stable | Fiberoptic laryngoscopy
|
| Iatrogenic vocal cord injury |
| Onset: within hours to days of extubation Severity and progression: variable | Fiberoptic laryngoscopy |
| Subglottis | |||
| Subglottic stenosis and subglottic cyst |
| Onset: congenital SGS may manifest at birth or later; acquired SGS or cysts may present within hours to days of laryngeal manipulation or extubation Severity and progression: variable | Laryngoscopy and bronchoscopy in operating room |
| Subglottic hemangioma |
| Onset: 4–6 weeks after birth Severity and progression: rapidly progressive within several months of diagnosis if not treated | Laryngoscopy and bronchoscopy in operating room |
| Trachea | |||
| Tracheomalacia |
| Onset: at birth if severe; may be within weeks to months Severity and progression: variable | Flexible tracheobronchoscopy during spontaneous respiration
|
| Vascular rings |
| Onset: at birth Severity: may be severe Progression: typically stable | CT or MR angiography
|
| Tracheal stenosis |
| Onset: at birth Severity and progression: variable | Laryngoscopy and bronchoscopy in operating room
|
Supraglottic Larynx
The presence of inspiratory stridor most often portends supraglottic obstruction. The supraglottis is involved with respiration and with airway protection during swallowing and as such has several moving parts.
Laryngomalacia is the inspiratory collapse of supraglottic soft tissues and accounts for most cases of neonatal stridor ( Fig. 67.2 ). Multiple etiologic theories have been proposed, with roles for supraglottic anatomic abnormalities, immature supraglottic cartilages, neuromotor abnormalities, or gastroesophageal reflux disease (GERD). One prospective study of 201 infants with laryngomalacia supports abnormal sensorimotor integrative function as an etiologic theory, with laryngeal tone and sensorimotor integrative function found to be altered and correlated with disease severity.
Laryngomalacia is characterized by high-pitched, inspiratory stridor that manifests within the first 2 weeks of birth. Stridor is exacerbated with agitation or exertion and typically worsens while supine and improves when prone or upright. Stridor may be associated with feeding difficulties (including coughing, choking, and regurgitation). Laryngomalacia often coexists with gastroesophageal reflux. One systematic review examining the relationship between laryngomalacia and gastroesophageal reflux found an overall reflux prevalence of 59% among infants with laryngomalacia, with three studies finding increased prevalence of reflux among infants with more severe laryngomalacia. However, a causal relationship with GERD and laryngomalacia cannot be inferred, at least with existing studies. Laryngomalacia may also coexist with other comorbidities including neurologic disease (such as seizure disorders, cerebral palsy, microcephaly, and Chiari malformation), synchronous secondary airway lesions (such as tracheomalacia or subglottic stenosis), congenital heart disease, or genetic disorders (commonly Down syndrome).
Laryngomalacia is characterized as mild, moderate, or severe based on the degree of airway obstruction and of feeding impairment. Most infants with laryngomalacia have mild disease, consisting of stridor without signs of respiratory difficulties (such as retractions, nasal flaring, tachypnea, etc.) and no major feeding symptoms. In the majority of infants with mild laryngomalacia, it resolves by age 12 to 18 months. Infants with moderate laryngomalacia have stridor that is associated with frequent feeding-related symptoms, including coughing, choking, and transient periods of respiratory distress. Infants with moderate laryngomalacia typically improve with acid suppression therapy and feeding modification strategies, including upright positioning or thickened feeds. Infants with severe laryngomalacia are those who have stridor associated with severe respiratory and feeding symptoms, including apneic spells, aspiration, recurrent cyanosis, and failure to thrive. Infants within this category often require surgical intervention.
Congenital laryngeal cysts are a rarer cause of supraglottic obstruction, with an estimated incidence of 1.8 to 3.5 per 100,000 live births. They may be saccular or ductal. Saccular cysts arise within the laryngeal saccule just above the vocal cords and may result from atresia or obstruction of the laryngeal ventricular opening. They may be contained to the larynx or may extend to extralaryngeal tissues. Ductal cysts result from obstruction of submucosal salivary ducts, leading to mucous-retention cysts. Vallecular cysts are a type of ductal cyst that arise within the space at the base of the tongue that marks the boundary between the pharynx and larynx. Vallecular cysts originate outside the supraglottis, but they can cause supraglottic obstruction by posterior displacement of the epiglottis ( Fig. 67.3 ). Histologic analysis of laryngeal cysts may reveal either squamous or respiratory epithelium.
Infants with congenital laryngeal cysts may present with inspiratory stridor and respiratory distress soon after birth. Infants with smaller cysts may not have significant stridor and may instead present later with feeding difficulties or incidentally. ,
Glottic Larynx
Vocal cord paralysis is the second most common cause of neonatal stridor. Vocal cord paralysis can be unilateral or bilateral, and it can be congenital or acquired. Congenital vocal cord paralysis may be related to anomalies of the central nervous system that cause dysfunction of the vagus nerve (such as Chiari malformation, hydrocephalus, or cerebral palsy) or idiopathic. Unilateral vocal cord paralysis is more likely to be acquired and may be associated with birth difficulties such as difficult forceps delivery or nuchal umbilical cord. Unilateral vocal cord paralysis can be seen after cardiothoracic surgery or treatment with extracorporeal membrane oxygenation therapy (ECMO), because these procedures can cause recurrent laryngeal nerve injury in the neck or the chest. , Bilateral and unilateral vocal cord paralysis have also been seen after periods of endotracheal intubation.
Infants with bilateral vocal cord paralysis may present with severe inspiratory or biphasic stridor and even respiratory distress. The cry is typically normal because the vocal cords usually can oppose, but they do not abduct for adequate respiration. Infants with unilateral paralysis rarely are distressed and they present with a hoarse cry.
Anterior glottic webs are a less common cause of neonatal stridor at the glottic level, accounting for approximately 5% of congenital laryngeal abnormalities ( Fig. 67.4 ). Glottic webs occur when the laryngeal lumen fails to recanalize during embryologic development, a process that occurs between weeks 8 and 10. Glottic webs range from mild (<35% of the glottis) to severe (up to 90% of the glottis); the degree of dysphonia and airway distress correlates with the extent of vocal cord involvement of the web. Additionally, large glottic webs can be associated subglottic stenosis. An estimated 65% of anterior glottic webs are associated with velocardiofacial syndrome, which occurs in 1 in 4000 live births, commonly associated with a deletion at chromosome 22q11.2. Laryngeal atresia may also occur, essentially a complete glottic web with life-threatening airway obstruction, requiring prompt heroic interventions.
Patients with glottic webs typically present with a hoarse voice and a degree of inspiratory or biphasic stridor shortly after birth. Severity of symptoms is dependent on the extent of vocal cord involvement. The Cohen classification categorizes glottic webs into type 1 (thin anterior web involving ≤35% of the glottis, which causes minimal airway obstruction); type 2 (thin or moderately thick anterior web involving 35%–50% of the glottis, which causes some airway obstruction); type 3 (thick anterior web involving 50%–75% of the glottis, often associated with subglottic narrowing and with moderately severe airway obstruction); and type 4 (thick glottic web involving up to 75%–90% of the glottis, with subglottic extension and severe airway obstruction).
Glottic obstruction may also result from injury from traumatic or prolonged intubation. Secondary glottic lesions related to intubation injury include vocal cord avulsion, glottic scar, granulomas, or paralysis.
Subglottic Larynx
Subglottic stenosis is the third most common cause of neonatal stridor. The subglottis contains the cricoid, which is the narrowest part of the neonatal airway and is the only complete cartilaginous ring in the airway. The cricoid is resistant to expansion, is not well vascularized, and is prone to scar formation after trauma. Congenital subglottic stenosis results from failure of airway recanalization through the cricoid cartilage, leading to malformation of the lumen or an abnormal relationship of the cricoid cartilage and the first tracheal ring. Congenital subglottic stenosis is commonly associated with genetic or syndromic diagnoses such as trisomy 21, CHARGE (coloboma, atresia choanae, retardation of growth, genitourinary abnormalities, and ear abnormalities) syndrome, and 22q11 deletion.
Acquired subglottic stenosis is nearly always related to endotracheal intubation ( Fig. 67.5 ). In older children, subglottic stenosis may also be associated with a history of a high tracheotomy, laryngeal burn, and neck trauma or tumors. Endotracheal tubes can cause pressure necrosis in the adjacent subglottis, and the resulting ulceration predisposes the area to infection or perichondritis. As the injured site heals by secondary intention, granulation tissue accumulates and a thick, fibrotic scar may result. The current risk of developing subglottic stenosis with appropriate endotracheal tube selection is estimated to be as low as 1% among neonates intubated longer than 48 hours. However, that risk increases with a larger endotracheal tube diameter; unexpected extubations, reintubations, or tube exchanges; excessive movement of the endotracheal tube (i.e., undersedation); duration of intubation; infection; and the presence of gastroesophageal reflux. ,
