Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable semi-upright radiograph of the chest demonstrates low lung volumes with resulting bronchovascular crowding . There is a stable - appearing retrocardiac opacity which may represent atelectasis , but superimposed infection can not be excluded . A small right - sided pleural effusion is present . No pneumothorax . Right internal jugular central venous line ends at the mid SVC .
    OUTPUT:
    
Stable retrocardiac opacity may represent atelectasis , but superimposed infection can not be excluded .