Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Chest , portable semi-upright . Again , lung volumes are low . There is a dense opacity obscuring the left hemidiaphragm . On the right , there is lower lobe atelectasis and chronic pleural thickening . There is no pneumothorax . The heart is enlarged but the extent is unknown secondary to the opacity .
    OUTPUT:
    
Dense retrocardiac opacity which could represent effusion , atelectasis , consolidation or a combination thereof .