Which radiographic finding is most consistent with atelectasis?

• A. Increased lung density with volume loss.
• B. Hyperinflation of the right lower lobe.
• C. Clear radiograph.
• D. Mediastinal shift toward the affected side.

Answer: (D)

Atelectasis causes loss of air-containing lung volume in the affected area, which shows up as increased density on the radiograph. But the telltale finding is that the mediastinal structures shift toward the side of the collapse. This inward pull happens because the collapsed lung loses volume and the remaining, aerated lung and chest wall pull the mediastinum toward the affected side. You’ll often also see the diaphragm on that side elevated and crowding of the neighboring lung tissue.

Hyperinflation of a lobe would suggest an obstructive or air-trapping process rather than collapse. A completely clear radiograph would not reflect the density increase seen with atelectasis. While increased density with volume loss is part of atelectasis, the directional shift of the mediastinum toward the affected side is the hallmark that best fits this condition.