Which statement about compression atelectasis is true?

• A. Mediastinum shifts toward the affected lung
• B. Pneumothorax is an example
• C. Associated with fibrotic changes
• D. It is not reversible

Answer: (B)

External pressure from air, fluid, or a mass compresses lung tissue, producing compression atelectasis. Because the collapse is due to outside compression, the mediastinum tends to shift away from the affected side on imaging. A pneumothorax is a classic cause of this external compression, so it clearly exemplifies compression atelectasis. The idea that the mediastinum shifts toward the collapsed side fits obstructive (resorptive) atelectasis, not compression. Fibrotic changes aren’t required for compression atelectasis and reflect chronic remodeling rather than the acute external compression itself. And relieving the external pressure typically reverses the collapse, so it is not correct to say it’s not reversible.