Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiomediastinal silhouette and pulmonary vasculature are unremarkable . There is an asymmetric left basilar , retrocardiac opacity . On the lateral view there is increased opacity in the retrocardiac region as well noting that this film demonstrates relatively lower lung volumes . Elsewhere , lungs are clear . There is no pleural effusion or pneumothorax . No acute osseous abnormalities .
    OUTPUT:
    
Retrocardiac opacity potentially atelectasis noting that infection is possible in the proper clinical setting .