Which radiologic finding is MOST characteristic of meconium aspiration syndrome on chest X-ray?

Explanation

## Radiologic Features of Meconium Aspiration Syndrome ### Characteristic CXR Appearance **Key Point:** The "salt-and-pepper" or patchy appearance with alternating areas of hyperinflation and atelectasis is the MOST characteristic finding in MAS. This reflects the ball-valve obstruction mechanism — some alveoli are over-distended (air trapping) while others are collapsed (distal obstruction). ### Classic Radiologic Findings in MAS | Finding | Frequency | Mechanism | |---------|-----------|----------| | Patchy infiltrates (salt-and-pepper) | ~60–70% | Ball-valve obstruction + atelectasis | | Hyperinflation (flattened diaphragm, increased AP diameter) | ~80% | Air trapping distal to obstruction | | Barrel-shaped chest | ~40% | Severe hyperinflation | | Air leak (pneumothorax, pneumomediastinum) | ~20–40% | Barotrauma from air trapping | | Lobar consolidation | <10% | Aspiration of thick meconium | ### Why Not the Other Options? **High-Yield:** - **Ground-glass opacities** are seen in RDS (surfactant deficiency), not MAS - **Lobar consolidation** suggests bacterial pneumonia or thick aspiration, not typical MAS - **Hyperinflation alone with clear fields** is seen in transient tachypnea of newborn (TTN), not MAS **Clinical Pearl:** The CXR appearance can evolve — early films may show only hyperinflation, while later films (24–48 hours) develop the characteristic patchy infiltrates as chemical pneumonitis develops. [cite:Nelson Textbook of Pediatrics 21e Ch 102]