Stridor and Congenital Airway Anomalies — Examination Question Bank

Applied Anatomy & Airway Dynamics

Question	Answer
1. What is Stridor and how does Bernoulli's Principle explain airway collapse?	- Stridor is a harsh, high-pitched, musical or vibratory respiratory sound produced by turbulent airflow passing through a narrowed or partially obstructed segment of the upper airway (from extrathoracic nose/pharynx down to the intrathoracic trachea). - Bernoulli's Principle: As air velocity increases across an anatomical constriction, the lateral pressure exerted by the gas against the airway wall decreases proportionally. - In infants, the airway cartilage is exceptionally compliant and pliable. During inspiratory suction, the drop in intraluminal lateral pressure creates a transmural gradient that pulls redundant supraglottic tissues inward into the laryngeal inlet, causing dynamic collapse (the fundamental mechanics of Laryngomalacia).
2. Differentiate Inspiratory, Biphasic, and Expiratory Stridor anatomically.
3. How does the cry / voice quality help localize the lesion?	- Normal, Clear, Crisp Phonatory Cry: The true vocal cords are normal and mobile $
ightarrow$ Lesion is Supraglottic (e.g., Laryngomalacia, vallecular cyst) or Infraglottic/Tracheal (e.g., Tracheomalacia). - Weak, Muffled, "Hot-Potato" Voice: Pharyngeal or supraglottic inflammatory mass (e.g., Retropharyngeal abscess, peritonsillar abscess, acute epiglottitis). - Hoarse, Breathy, or Aphonic Cry: Direct vocal cord pathology $
ightarrow$ Glottic level (e.g., Vocal cord paralysis, laryngeal papillomatosis, laryngeal web). - Brassy, "Barking / Seal-like" Cough: Subglottic level (e.g., Croup, subglottic stenosis).

Laryngomalacia & Endoscopic Evaluation

Question	Answer
4. What is Laryngomalacia and what are its classical dynamic laryngoscopic findings?	Laryngomalacia is the most common congenital anomaly of the larynx ($60-70\%$ of all congenital stridor) and the leading cause of stridor in early infancy. - Caused by delayed neuromaturation of laryngeal tone and floppy cartilaginous framework. - Laryngoscopic Hallmarks: 1) Inward prolapse of elongated, curled, tubular omega-shaped ($\Omega$) epiglottis on inspiration. 2) Inward collapse of massive, redundant arytenoid mucosa and cuneiform/corniculate cartilages. 3) Shortened aryepiglottic folds that tether the epiglottis posteriorly. - Dynamic Behavior: Stridor appears at 2-4 weeks of life, peaks at 6-8 months, is worst in the supine position and during feeding/crying, and significantly diminishes in the prone position with neck extended. Resolves spontaneously in $>90\%$ by 18-24 months.
5. What is the gold standard diagnostic modality for infant stridor?	Awake Flexible Fiberoptic Laryngoscopy (FFL): - Performed transnasally without general anesthesia or sedation. - Why Awake? Sedation or general anesthesia abolishes intrinsic laryngeal muscular tone and spontaneous respiratory excursions, preventing dynamic assessment of inspiratory collapse and vocal cord mobility! - Evaluates the entire dynamic respiratory cycle, ruling out synchronous secondary airway lesions (present in $10-15\%$).
6. What are the indications for Surgical Intervention (Supraglottoplasty)?	While $>85-90\%$ of laryngomalacia is mild and self-limiting, severe laryngomalacia ($10-15\%$) requires surgical Supraglottoplasty (microlaryngoscopy with cold scissors, laser, or microdebrider). Indications include: 1) Severe respiratory distress with persistent suprasternal and subcostal retractions at rest. 2) Failure to thrive / growth faltering due to excessive work of breathing. 3) Feeding difficulties: Choking, sputtering, recurrent aspiration pneumonias. 4) Obstructive sleep apnea with hypoxemia or hypercapnia. 5) Development of progressive pectus excavatum or pulmonary hypertension (cor pulmonale).

Other Airway Anomalies, Hemangiomas & Viva Traps

Question	Answer
7. Describe Congenital Subglottic Stenosis and the Myer-Cotton Grading System.	Congenital narrowing of the subglottic lumen (defined as diameter $<4.0 ext{ mm}$ in a term infant or $<3.0 ext{ mm}$ in a premature infant at the cricoid ring) without prior history of intubation. - Myer-Cotton Grading System (Endoscopic cross-sectional area reduction): - Grade I: $<50\%$ obstruction of lumen. - Grade II: $51\% - 70\%$ obstruction. - Grade III: $71\% - 99\%$ obstruction (detectable lumen present). - Grade IV: $100\%$ obstruction (no detectable lumen; complete atresia).
8. How do you diagnose and medically manage Subglottic Hemangioma?	- Proliferating vascular lesion in the subglottic space; manifests as biphasic stridor between 4 weeks and 6 months of life. - Cutaneous Marker: $50\%$ of infants have concomitant cutaneous infantile hemangiomas, particularly in a "beard distribution" (mandible, lower lip, chin, neck). - Medical Treatment of Choice: Oral Propranolol ($2-3 ext{ mg/kg/day}$ divided bid). Propranolol induces vasoconstriction, downregulates VEGF and bFGF, and triggers capillary endothelial apoptosis, resulting in dramatic regression of the subglottic mass within weeks, avoiding tracheostomy!
9. VIVA TRAP: What is the cardinal danger of sedating or instrumenting an infant with acute severe stridor?	VIVA TRAP: Never attempt sedatives, muscle relaxants, blind oral suctioning, or rigid instruments without a fully secured airway operating room setting! - An infant with borderline airway compromise relies on active voluntary accessory muscle contraction and pharyngeal dilator tone to maintain airway patency. - Sedation abolishes muscle tone, precipitating immediate, catastrophic total airway collapse and cardiac arrest. Direct visualization in acute stridor must be done awake via flexible fiberoptic scope, or under controlled inhalational anesthesia in the OR with ENT and ECMO/rigid bronchoscopy standby!
10. Counter-Question Chain: "How do you differentiate Laryngomalacia from Tracheomalacia clinically and endoscopically?"	- Clinical: Laryngomalacia produces high-pitched inspiratory stridor that improves prone and worsens supine; voice and cough are normal. Tracheomalacia produces low-pitched expiratory stridor / wheeze or a harsh, barking, "seal-like" expiratory cough that worsens during coughing, feeding, or crying (intrathoracic positive pressure collapses the trachea). - Endoscopy: Laryngomalacia shows dynamic supraglottic collapse on inspiration. Tracheomalacia shows $>50\%$ dynamic reduction in tracheal luminal cross-sectional area during expiration on flexible tracheobronchoscopy.