A 2-hour-old term newborn with meconium-stained amniotic fluid presents with tachypnea (RR 68/min), grunting, and intercostal retractions. Which is the most common radiographic finding on chest X-ray in meconium aspiration syndrome?

## Radiographic Findings in Meconium Aspiration Syndrome **Key Point:** The classic CXR pattern in MAS is **patchy infiltrates interspersed with areas of hyperinflation and atelectasis** — a mixed picture reflecting the underlying ball-valve obstruction mechanism. ### Characteristic Chest X-Ray Pattern | Finding | Cause | Frequency | |---------|-------|----------| | **Patchy infiltrates** | Meconium-filled alveoli and inflammatory exudate | Very common | | **Hyperinflation** | Air trapping distal to obstructed airways (ball-valve effect) | Very common | | **Atelectasis** | Complete obstruction of small airways | Common | | **Barrel chest** | Severe hyperinflation; flattened diaphragms | Moderate | | **Pneumothorax** | Rupture of overdistended alveoli | 10–40% of cases | | **Pneumomediastinum** | Air dissection along bronchovascular sheaths | 5–15% of cases | **High-Yield:** The **mixed pattern of infiltrates + hyperinflation** is pathognomonic for MAS and distinguishes it from other causes of neonatal respiratory distress: - RDS (HMD) → diffuse ground-glass opacities with air bronchograms - Pneumonia → lobar or segmental consolidation - Transient tachypnea → perihilar streaking (fluid in interlobar fissures) ### Clinical Correlation **Clinical Pearl:** The degree of radiographic hyperinflation often exceeds the clinical severity — some infants with severe CXR hyperinflation may have mild symptoms, while others with moderate findings may deteriorate rapidly. This is because air trapping can mask underlying atelectasis. ### Why This Pattern Occurs Meconium particles lodge in small airways, creating a **ball-valve obstruction**: 1. Air enters distally during inspiration (valve opens) 2. Air cannot escape during expiration (valve closes) 3. Progressive air trapping → hyperinflation 4. Surrounding alveoli collapse due to obstruction → atelectasis 5. Result: **patchy infiltrates mixed with hyperinflation** ### Progression Early CXR (first 6 hours) may show only mild infiltrates; hyperinflation becomes more apparent as air trapping progresses over 12–24 hours.