Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest . There is faint retrocardiac opacity which could potentially be due to atelectasis . Elsewhere , the lungs are clear . The cardiomediastinal silhouette is stable . Tortuous descending thoracic aorta is seen . No acute osseous abnormality is identified .
    OUTPUT:
    
Retrocardiac opacity , potentially atelectasis given lower lung volumes , noting that infection can not be entirely excluded . Otherwise , unremarkable chest x-ray .