A 3-year-old child presents with acute onset stridor and cyanosis after playing with peanuts. Chest X-ray shows hyperinflation of the right lung with mediastinal shift. Which feature best distinguishes a foreign body aspiration from acute epiglottitis in this clinical scenario?

Explanation

## Distinguishing Foreign Body Aspiration from Acute Epiglottitis ### Key Radiological Discriminator **Key Point:** Unilateral hyperinflation with mediastinal shift is pathognomonic for foreign body aspiration and does NOT occur in epiglottitis. ### Pathophysiology Comparison | Feature | Foreign Body Aspiration | Acute Epiglottitis | |---------|------------------------|--------------------| | **Onset** | Sudden (witnessed choking event) | Gradual (hours) | | **Fever** | Absent initially | High fever (>38.5°C) | | **Stridor type** | Biphasic or expiratory | Inspiratory | | **Chest X-ray** | Unilateral hyperinflation, mediastinal shift | Normal or subglottic narrowing ("thumb sign") | | **Cough** | Paroxysmal, triggered by FB | Absent or minimal | | **Drooling** | Absent | Prominent ("hot potato" voice) | | **Positioning** | Varies; child may be comfortable | Tripod position, refuses to lie flat | ### Why Unilateral Hyperinflation is the Best Discriminator **High-Yield:** The mechanism is **ball-valve obstruction** — the foreign body acts as a one-way valve, allowing air in during inspiration but trapping it during expiration. This causes progressive hyperinflation of the distal lung, pushing the mediastinum to the contralateral side. **Clinical Pearl:** In epiglottitis, the swelling is supraglottic and bilateral, so chest X-ray shows either normal lungs or symmetric findings. Mediastinal shift never occurs because there is no unilateral air-trapping. ### Diagnostic Confirmation **Tip:** Expiratory or decubitus chest X-rays in suspected FB aspiration will show the hyperinflated lung fail to collapse, confirming the diagnosis. In epiglottitis, both lungs deflate symmetrically. [cite:Cummings Otolaryngology 7e Ch 193]