Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Left retrocardiac opacity may represent atelectasis , although infection or aspiration could be considered in the appropriate clinical setting . No other consolidation . No pleural effusion or pneumothorax . Cardiomediastinal contours are normal . No subdiaphragmatic free air . No acute osseous abnormalities identified .
    OUTPUT:
    
Left retrocardiac atelectasis versus infection / aspiration .