Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright portable chest radiograph was provided . Lung volumes are low . There is blunting at the left CP angle which could represent a left pleural effusion . Bibasilar linear opacities are most compatible with pneumonia in the setting of low lung volumes . The heart appears mildly enlarged . Mediastinal contour appears normal . No pneumothorax is seen . Bony structures appear grossly intact , though cortical irregularity involving the subacromial space bilaterally though incompletely imaged .
    OUTPUT:
    
Small left pleural effusion with bibasilar linear opacities which most likely represent atelectasis . Please note , pneumonia can not be entirely excluded . Degenerative changes in the subacromial region bilaterally at the shoulders .