An air bronchogram is a classic sign of alveolar consolidation. It occurs when the alveoli surrounding the bronchi are filled with fluid or exudate, making the air-filled bronchi visible as lucent branching structures against the background of the opacified lung parenchyma. Kerley B lines indicate interstitial edema, pleural effusion is fluid in the pleural space, and hilar lymphadenopathy suggests enlarged lymph nodes in the hilum, none of which are direct signs of alveolar consolidation.
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