Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are unchanged compared to the prior study . The trachea is central . The cardiomediastinal contour is unchanged . The heart is mildly enlarged , similar in appearance when compared to the prior study . Streaky retrocardiac opacities are likely due to a atelectasis in the left lower lobe . Infection can not be excluded . No pulmonary vascular congestion or pulmonary edema appreciated . No pleural effusion seen .
    OUTPUT:
    
Retrocardiac opacities in likely reflect left lower lobe atelectasis but infection can not be excluded .