Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are low , and the patient is slightly rotated . There is a new retrocardiac opacity which obscures the left hemidiaphragm . No other focal opacities are identified . There is no pulmonary edema , pleural effusion , or pneumothorax . The aorta is tortuous and calcified , unchanged from prior exams . The heart size is mildly enlarged , and also unchanged from prior exams .
    OUTPUT:
    
Retrocardiac opacity . This may represent infection or atelectasis .