On chest radiography, which finding is classic for a pneumothorax?

• A. Cardiac enlargement
• B. Widened mediastinum
• C. Diffuse edema
• D. Hyperlucency with absent vascular markings on the affected side

Answer: (D)

Pneumothorax shows up on chest radiographs as an area of increased radiolucency where there are no air-filled lung vessels—the space outside the edge of the lung appears darker because air in the pleural space blocks X-ray transmission. The boundary of the collapsed lung is seen as a visceral pleural line, and beyond that line you don’t see the normal pulmonary vessels. This combination—hyperlucency with absent vascular markings on the side of the collapse—is the classic sign.

The other findings point to different problems: cardiac enlargement suggests enlarged heart size, not a pneumothorax; a widened mediastinum indicates mediastinal pathology rather than air in the pleural space; and diffuse edema shows increased vascular markings from fluid overload, not a loss of markings due to air.