Stridor

Basics

Description

  • High-pitched audible wheezing and vibratory harsh sounds mainly on inspiration
  • Impedance of air movement through the upper airway
  • It implies a laryngotracheal airway obstruction
  • Inspiratory stridor:
    • Occurs due to extrathoracic airway obstruction (above the thoracic inlet)
    • During inspiration, the pressure inside the airway falls below atmospheric pressure, leading to airway collapse
    • The Bernoulli effect contributes to further narrowing and turbulent airflow
    • High pitched, loudest over the neck, worsens with crying, improves with neck extension, suggests supraglottic or glottic obstruction
  • Expiratory stridor:
    • Occurs due to intrathoracic airway obstruction (below the thoracic inlet, typically in the trachea or bronchi)
    • During expiration, intrathoracic pressure rises, causing dynamic airway collapse if the structural integrity is weak
    • Low pitched, best heard over the chest, worsens with forced expiration, improves prone, suggests intrathoracic airway collapse
  • Biphasic stridor:
    • Indicates a fixed, central airway obstruction, usually involving the subglottic area or upper trachea
    • Both inspiratory and expiratory airflow is disrupted due to a rigid narrowing of the airway lumen
    • Low pitched, best heard over the chest, worsens with forced expiration, improves prone, suggests intrathoracic airway collapse
  • Stridor is significantly more common in pediatric populations
  • Viral croup causes 90% of all cases of stridor in children:
    • Strong seasonal pattern, peaking in late fall and early winter

Etiology

Pediatric

  • Congenital causes:
    • Laryngomalacia (most common congenital cause of inspiratory stridor)
    • Laryngeal webs/rings
    • Vascular anomalies (eg, vascular rings, pulmonary artery sling)
    • Congenital subglottic stenosis
    • Laryngeal cysts
    • Laryngotracheoesophageal clefts
    • Congenital vocal cord dysfunction
    • Unilateral or bilateral vocal cord paralysis
    • Neural abnormalities (eg, meningomyelocele, Arnold–Chiari malformation)
    • Congenital myopathies affecting vocal cord function
    • Subglottic hemangioma
    • Tracheomalacia
  • Infectious causes:
    • Bacterial tracheitis
    • Epiglottitis
    • Viral croup
    • Peritonsillar abscess
    • Retropharyngeal abscess
    • Supraglottitis
    • Uvulitis
    • Ludwig angina
    • Diphtheria
    • Tetanus
    • COVID-19 laryngotracheitis
  • Inflammatory and autoimmune causes:
    • Recurrent respiratory papillomatosis
    • Granulomatosis with polyangiitis
    • Relapsing polychondritis
    • Sarcoidosis
    • Eosinophilic granulomatosis with polyangiitis
  • Extrinsic compression causes:
    • Hematoma
    • Neck trauma
    • Enlarged lymph nodes
    • Mediastinal mass
    • Thyroid masses/carcinomas
    • Cervical vertebral abnormalities
  • Mechanical obstruction (intraluminal):
    • Foreign body aspiration
    • Intraluminal tumors:
      • Squamous cell carcinoma
      • Lymphomas
      • Laryngeal or tracheal papilloma
    • Subglottic stenosis:
      • Congenital
      • Postoperative scarring
      • After radiation therapy
      • After prolonged endotracheal intubation
  • Vocal cord dysfunction (pediatric and adult):
    • Congenital vocal cord dysfunction
    • Paradoxical vocal fold movement disorder (PVFMD)
    • Postintubation trauma
    • Surgical injury (eg, thyroidectomy)
    • Neurogenic causes (stroke, Parkinson, multiple system atrophy)
    • Thyroid malignancy

Adult

  • Structural and mechanical causes:
    • Tracheomalacia
    • Postintubation subglottic stenosis
    • Laryngeal or tracheal tumors
    • Vocal cord paralysis
    • Postsurgical trauma
    • Radiation-induced laryngeal fibrosis
    • Anaphylaxis and angioedema
    • Tracheal stenosis from autoimmune conditions
  • Extrinsic compression:
    • Goiter or thyroid masses
    • Mediastinal tumors
    • Hematoma
  • Infectious and inflammatory causes:
    • Bacterial tracheitis
    • Epiglottitis
    • Laryngopharyngeal reflux
    • Invasive fungal infections (mucormycosis in immunocompromised patients)
  • Neuromuscular disorders:
    • Multiple system atrophy
    • Parkinson disease–related vocal cord dysfunction
    • Amyotrophic lateral sclerosis
    • Myasthenia gravis

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