Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest demonstrate low lung volumes , which accentuate bronchovascular markings . Retrocardiac opacity is noted . Left hemidiaphragm is obscured on the frontal view . No large pleural effusion . No pneumothorax . Hilar and mediastinal silhouettes are unremarkable . The heart size is top normal .
    OUTPUT:
    
Low lung volumes . Retrocardiac opacity , likely atelectasis . However , superimposed infection can not be excluded .