label: Air bronchogram
label_lc: air bronchogram
description: "An air bronchogram is a pattern of air-filled (low-attenuation) bronchi on a background of opaque (high-attenuation) airless lung. The sign implies (a) patency of proximal airways and (b) evacuation of alveolar air by means of absorption (atelectasis) or replacement (eg, pneumonia) or a combination of these processes. In rare cases, the displacement of air is the result of marked interstitial expansion (eg, lymphoma)."