Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest were reviewed and compared to the prior study . There is a retrocardiac opacity . Mild blunting of the left costophrenic angle could represent a tiny pleural effusion or pleural thickening . Cardiac and mediastinal contours are normal and there is no vascular congestion or pneumothorax . There are no concerning osseous or soft tissue lesions .
    OUTPUT:
    
Retrocardiac opacity consistent with left lower lobe pneumonia .