Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral chest radiograph demonstrates a new retrocardiac opacity with obscuration of the left hemidiaphragm . While this may reflect a component of atelectasis , an infection can not be excluded . There is likely a small left pleural effusion . The right lung remains clear with linear platelike atelectasis within the right lower lobe . Allowing for the decreased lung volumes when compared to prior radiograph dated ___ , the cardiomediastinal and hilar contours appear stable .
    OUTPUT:
    
1 . New retrocardiac opacification which may reflect a component of atelectasis , though pneumonia is not excluded . 2 . Small left sided pleural effusion . 3 . Allowing for lower lung volumes , the cardiomediastinal and hilar silhouettes appear stable .