Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable semi-upright view of the chest demonstrates low lung volumes . Retrocardiac opacity partially obscures left hemidiaphragm . Left costophrenic angle is obscured , suggestive of small pleural effusion . The right lung is clear . Hilar and mediastinal silhouettes are unremarkable . Heart size is normal . There is no pulmonary edema . Partially imaged abdomen is unremarkable .
    OUTPUT:
    
Retrocardiac opacity , may represent atelectasis or infection in the appropriate clinical setting .