Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP and lateral views of the chest were obtained with patient positioned upright . There is left basilar linear density with volume loss most likely reflecting atelectasis , though an early pneumonia is difficult to exclude in the right clinical setting . No large effusion or pneumothorax is seen . The cardiomediastinal silhouette is notable for an unfolded thoracic aorta with atherosclerotic calcifications . No definite bony abnormalities are seen .
    OUTPUT:
    
Vague opacity at the left lung base which likely represents atelectasis , though an early pneumonia not excluded .