Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest . Equivocal retrocardiac opacity appears to project over the lower thoracic spine on the lateral view . No pleural effusion or pneumothorax . Heart size and cardiomediastinal contours are normal .
    OUTPUT:
    
Equivocal retrocardiac opacity could represent atelectasis or pneumonia in the appropriate clinical setting .