Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . Retrocardiac opacity with obscuring of the lateral border of the thoracic aorta on the frontal view and better seen on the lateral view with a spine sign may represent round atelectasis , although an acute process such as pneumonia can not be completely excluded . Linear plate - like band in the left lower lung is atelectasis . No pleural effusion . No pneumothorax . The heart is normal in size . No pulmonary edema .
    OUTPUT:
    
Retrocardiac opacity may reflect round atelectasis , however acute pneumonia can not be excluded and recommend treatment with follow - up chest radiograph to ensure resolution .