A fiberoptic light is place on an infant's right chest. A lighted halo is seen around the point of contact. The light is then placed on the infant's left chest and no light can be seen. This would indicate that

• A. The right hemidiaphragm is absent
• B. There is a right pneumothorax
• C. There is a pneumomediastinum present
• D. The left hemidiaphragm is herniated

Answer: (D)

Transillumination relies on how light passes through chest tissues. Air-filled lung transmits light differently than solid or fluid-filled structures. Seeing a light halo when the light is on the right chest means the right thorax has air-filled, relatively translucent lungs. The absence of any light when the light is placed on the left chest means the left thorax is not translucent, most consistent with abdominal contents herniating into the chest and displacing or replacing the left lung.

This pattern points to a left congenital diaphragmatic hernia, where stomach or bowel sits in the left chest. Left-sided CDH is more common because the liver on the right offers some protection. If it were a pneumothorax on the left, you’d expect increased light transmission on that side, not a lack of light. Imaging would follow to confirm.