What are the causes of stridor?

Causes of Stridor

Stridor is primarily caused by obstruction of the upper airways, with laryngomalacia being the most common cause in children, while other causes include vocal cord paralysis, congenital anomalies, foreign body aspiration, and exercise-induced laryngeal disorders. 1, 2

Common Congenital Causes

• Laryngomalacia: The most common congenital laryngeal anomaly and the most frequent cause of persistent stridor in children, characterized by diminished laryngeal tone resulting in supraglottic collapse 1
• Vocal cord paralysis: The third most common congenital laryngeal anomaly producing stridor in infants and children, usually resulting from congenital anomalies of the central nervous system 1, 2
• Other congenital laryngeal anomalies:
  • Laryngoceles and saccular cysts 1
  • Laryngeal webs and atresia 1
  • Laryngotracheal stenosis 1, 3
  • Laryngeal and tracheal clefts 1
  • Congenital neoplasms (e.g., hemangiomas) 1
  • Bifid epiglottis and ventral cleft of the larynx 1
• Vascular anomalies: Vascular rings that can compress the trachea/esophagus, manifesting as stridor 1, 3

Common Acquired Causes

• Foreign body aspiration: Causes localized monophonic wheeze and stridor 1, 4
• Exercise-induced laryngeal disorders (EILD):
  • Paradoxical vocal cord dysfunction (VCD) 1
  • Exercise-induced laryngeal prolapse 1
  • Exercise-induced laryngomalacia 1
• Infections:
  • Viral croup (most common cause of acute stridor in young children) 4
  • Epiglottitis (true pediatric emergency) 4
  • Bacterial tracheitis 4
  • Retropharyngeal abscess 4
• Allergic airway edema 4
• Gastroesophageal reflux: Can contribute to laryngeal abnormalities and stridor 1

Diagnostic Approach Based on Stridor Characteristics

By Timing in Respiratory Cycle

• Inspiratory stridor: Usually indicates obstruction at supraglottic or glottic level 5
• Expiratory stridor: Typically originates from obstruction at or below glottic level 5
• Biphasic stridor: Suggests severe upper airway obstruction 5

By Age of Presentation

• Neonates and infants: Laryngomalacia, vocal cord paralysis, and subglottic stenosis are most common 3
• Older children: Stridor is rare but always warrants endoscopy if not due to recent endotracheal intubation 1

By Onset Pattern

• Acute onset: Often viral croup (particularly during fall and early winter), foreign body aspiration, epiglottitis, or bacterial tracheitis 4
• Chronic stridor: Usually laryngomalacia in infants (resolves by second year of life), subglottic hemangioma, or vocal cord paralysis in older children 4

Diagnostic Evaluation

• Flexible bronchoscopy/laryngoscopy: The diagnostic procedure of choice for evaluating stridor, allowing examination of laryngeal structure and function during inspiration and expiration 1, 2
• Imaging studies:
  • Airway radiographs for initial assessment 4
  • Barium studies to rule out vascular compression 4, 3
  • Angiotomography to diagnose vascular rings 3
• Flow-volume loops: May show flattening or truncation of the inspiratory portion in vocal cord dysfunction 1

Important Clinical Considerations

• Abnormalities below the epiglottis are found in up to 68% of cases, making it important to inspect both upper and lower airways 1
• Stridor in older children is rare but always warrants endoscopy if not due to recent endotracheal intubation 1
• Exercise-induced laryngeal disorders present with inspiratory stridor during exercise that resolves within 5 minutes of stopping, contrasting with exercise-induced bronchoconstriction which peaks 5-20 minutes after exercise 1
• Laryngeal cleft may be missed by flexible bronchoscopy, and rigid bronchoscopy should be performed if this diagnosis is suspected 1

Management Approach

Management depends on the underlying cause and severity of symptoms, ranging from observation for mild laryngomalacia to immediate intervention for life-threatening obstruction 2, 4.