In lobar pneumonia, which radiographic sign indicates air-filled bronchi within dense alveolar consolidation?

• A. Kerley lines
• B. Air bronchograms
• C. Pleural effusion
• D. Pulmonary edema

Answer: (B)

Air bronchograms occur when alveoli are filled with inflammatory exudate in lobar pneumonia, while the bronchi remain open and filled with air. On the radiograph this creates dark, air-filled, branching or tubular structures that contrast against the surrounding opaque, dense consolidation. This contrast is what makes air bronchograms a classic sign of alveolar (lobar) pneumonia, helping to differentiate it from other causes of opacity.

Kerley lines are thin, horizontal lines from thickened interlobular septa seen in interstitial edema or atelectasis, not within consolidated airways. Pleural effusion shows fluid layering and meniscus signs at the edges of the lung, not air-filled bronchi within a dense lump of opacity. Pulmonary edema typically presents with diffuse interstitial markings and vascular congestion, rather than the distinct air-filled bronchi within consolidation.

So the presence of air-filled bronchi within a dense area of lung opacity directly points to air bronchograms, signaling alveolar consolidation from lobar pneumonia.