Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is somewhat increased left base retrocardiac opacity worrisome for pneumonia . No pleural effusion is seen . The right lung is clear . There is no evidence of pneumothorax . The cardiac and mediastinal silhouettes are stable and unremarkable .
    OUTPUT:
    
Left lower lobe retrocardiac opacity , somewhat increased as compared to the prior study , is concerning for pneumonia .