Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Single supine chest radiograph was obtained . There is a new left retrocardiac opacity and the leftward mediastinal shift . The right lung is well expanded and clear . There is no pneumothorax . Cardiac size is normal .
    OUTPUT:
    
Left lower lobe collapse and possible left pleural effusion . Additional element of infection can not be excluded .