Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest demonstrates a retrocardiac opacity projecting posteriorly on lateral view , consistent with a left lower lobe pneumonia . The right lung is clear . There is no change to a tortuous descending aorta . The cardiomediastinal and hilar contours are stable . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Left retrocardiac opacity , consistent with a left lower lobe pneumonia . Recommend followup chest radiograph in ___ weeks after treatment to assess for resolution .