Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral images of the chest . The lungs are well expanded . There is a retrocardiac opacity which likely represents atelectasis , but can not rule out pneumonia or aspiration in the right clinical setting . There is no pleural effusion or pneumothorax . The cardiomediastinal silhouette is unremarkable . Indication on the right aspect of the trachea is again seen , possibly related to a prominent right thyroid lobe .
    OUTPUT:
    
Opacity in the left lower lobe , likely representing atelectasis , but can not rule aspiration or pneumonia in the right clinical setting .