A transillumination of an infant's right chest results in the entire side becoming lit up. What does this indicate?

The scenario described indicates that transillumination of the infant's right chest resulted in the entire side being lit up. This finding is characteristic of a pneumothorax. When air is present in the pleural space, it allows light to pass through more freely than it would in normal lung tissue or fluid-filled spaces. This radiolucency, or increased light transmission, signifies the presence of air rather than solid or liquid matter, suggesting that the lung is not fully expanded.

In contrast, other conditions like pneumomediastinum typically would not cause the entire chest side to illuminate; instead, it might produce less diffuse effects. A normal chest would not show such pronounced transillumination, as the presence of normal lung tissue would absorb the light. While abdominal distension may lead to some respiratory symptoms, it does not relate to the transillumination of the chest itself. Thus, the indication of a pneumothorax aligns with the clinical presentation observed in the transillumination test.