Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size , mediastinal , and hilar contours are normal . There is an opacity in the left lower lung , extending into the left retrocardiac region . Given the patient 's clinical history , this is concerning for pneumonia . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Opacity in the left lower lung and retrocardiac region this concerning for pneumonia , given the patient 's clinical history .