Which radiographic sign suggests a pneumothorax on chest radiographs?

• A. Cardiomegaly
• B. Pleural effusion
• C. Interstitial edema
• D. Absence of lung markings and a visceral pleural line; apical lucency

Answer: (D)

Pneumothorax on chest radiographs is suggested by a visible visceral pleural line with no lung markings beyond it, accompanied by increased radiolucency in the space outside the line. That line marks the edge of the collapsed lung, and air in the pleural space prevents the usual lung markings from being seen distal to it. The apical lucency is the air collecting in the pleural space, often most evident at the apex.

This pattern is what distinguishes pneumothorax from other findings: cardiomegaly would show an enlarged heart, pleural effusion would produce a fluid level and blunting of the costophrenic angles, and interstitial edema leads to diffuse hazy markings rather than a sharp edge and absent markings beyond it. In practice, small pneumothoraces can be subtle, but the hallmark is the visceral pleural line with absence of peripheral lung markings and apical air.