Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear stable . There is new confluent retrocardiac opacification with a probable small pleural effusion on . Otherwise , the lungs appear clear .
    OUTPUT:
    
New left basilar opacification , typical for atelectasis , in association with suspected pleural effusion ; infectious process is not excluded but less likely , however .