Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear unchanged . There is no pleural effusion or pneumothorax . There is a retrocardiac opacity that is not specific obscuring medial left hemidiaphragmatic contours . Otherwise the lungs appear clear .
    OUTPUT:
    
Left lower lobe opacity , which could be seen with atelectasis , although an infectious process is not excluded and results should be correlated with clinical presentation . No evidence of congestive heart failure .