Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Low lung volumes . Linear opacities at right lung base reflect atelectasis . Patchy opacification at left lung base silhouetting the left hemidiaphragm . The lungs are otherwise clear . Heart size is normal . The mediastinal and hilar contours are normal . The pulmonary vasculature is normal . No pleural effusion or pneumothorax is seen . There are no acute osseous abnormalities .
    OUTPUT:
    
Low lung volumes with bibasilar atelectasis , however underlying pneumonia can not be ruled out .