Which radiographic feature is characteristic of a pneumothorax on chest X-ray?

• A. Increased opacity due to edema
• B. Bilateral pleural effusions
• C. Interstitial edema
• D. Hyperlucency with absence of vascular markings on the affected side

Answer: (D)

Recognizing a pneumothorax on chest X-ray hinges on spotting air in the pleural space, which shows up as increased (dark) lucency on the affected side with a distinct visceral pleural line. Beyond this line there are no lung markings because there is no lung tissue there. This appearance is what sets pneumothorax apart from edema or effusions, which create increased opacity or blurred costophrenic angles rather than a dark, air-filled space. So the key feature is hyperlucency with absence of vascular markings on the side of the pneumothorax, often with a visible pleural edge.