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Difficulty: MediumPediatric Respiratory Disorders

During a scheduled wellness visit, the parents of a 4-month-old infant express concern regarding their child's breathing. They describe a high-pitched 'squeaking' sound when the baby inhales, which they first noticed around 4 weeks of age. The noise becomes significantly louder when the infant is crying or placed on his back to sleep. Conversely, the parents note the sound almost completely disappears when the baby is resting on his stomach. He is exclusively breastfed, feeds well without cyanosis or choking, and is tracking along the 50th percentile for both length and weight. His temperature is 37.0°C (98.6°F), pulse is 120/min, and respirations are 30/min. Physical examination reveals an alert, well-nourished infant with prominent inspiratory stridor that worsens in the supine position. Which of the following is the most likely underlying cause of this patient's clinical presentation?

  1. Collapse of the supraglottic structures during inspirationAnswer
  2. B
    Abnormal development of the aortic arch system
  3. C
    Viral-induced edema of the subglottic space
  4. D
    Bacterial invasion of the supraglottic tissues
  5. E
    Fixed fibrotic narrowing of the subglottic airway

Answer

The correct answer is the collapse of the supraglottic structures during inspiration, which is the underlying mechanism of laryngomalacia.
The correct answer accurately describes the pathophysiology of laryngomalacia. Laryngomalacia is the most common cause of stridor in infants. It is caused by delayed maturation and excessive flaccidity of the supporting cartilage of the supraglottic airway, leading to an inward collapse during the negative pressure of inspiration. The classic presentation is inspiratory stridor that is exacerbated by crying, feeding, or lying supine, and relieved by lying prone. Because the infant is thriving, management involves reassurance, as symptoms typically resolve spontaneously by 12 to 18 months of age.

Step-by-Step Solution

1
Analyze the patient's presentation and timeline.
A 4-month-old infant presents with chronic inspiratory stridor starting at 4 weeks of age that worsens in the supine position and with agitation, but improves in the prone position.
Identifying the onset, phase of respiration (inspiratory), and modifying factors (positional) is critical for differentiating causes of pediatric stridor.
2
Evaluate for severity and secondary complications.
The infant is feeding well, gaining weight appropriately (50th percentile), and has normal vital signs without fever or distress.
Rules out acute infectious emergencies (like epiglottitis) and structural anomalies that impair feeding (like vascular rings).
3
Synthesize findings to establish a diagnosis.
The classic timeline and positional nature of the stridor (worse supine, better prone) in a thriving infant are pathognomonic for laryngomalacia.
Laryngomalacia is the most common cause of infantile stridor and can be diagnosed clinically based on these classic features.
4
Identify the underlying pathophysiology of the diagnosed condition.
Laryngomalacia is characterized by increased laxity and collapse of the supraglottic structures during the negative pressure of inspiration.
Matches the clinical picture to the anatomical defect requested by the question.

Key Concept

Laryngomalacia presents with inspiratory stridor that worsens in the supine position and improves when prone, caused by the collapse of floppy supraglottic structures during inspiration.
Estimated Time:1m 0s
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Topics

Pediatric Respiratory Disorders

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