Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest were obtained . There are relatively low lung volumes . A subtle left base retrocardiac opacity most likely represents atelectasis and confluence of vessels ; however , an early infectious process is not excluded in the appropriate clinical setting . The right lung is clear . There is no pleural effusion or pneumothorax . The cardiac and mediastinal silhouettes are unremarkable . No pulmonary edema is seen .
    OUTPUT:
    
Subtle patchy posterior left lower lobe opacity , most likely represents atelectasis and overlap of vascular structures , although infection is not excluded in the appropriate clinical setting .