Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There are low lung volumes . The cardiomediastinal silhouette is unchanged , reflective of a top - normal heart size . The hila are unremarkable . There is retrocardiac opacity which is new since prior exam and concerning for pneumonia . Elsewhere , the lungs are clear . There is no pulmonary venous congestion . There is no pneumothorax or pleural effusion .
    OUTPUT:
    
New retrocardiac opacity is concerning for left lower lobe pneumonia .