Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is normal . Mediastinal and hilar contours are unremarkable . The pulmonary vascularity is normal . A focal opacity within the retrocardiac region is concerning for left lower lobe pneumonia . No pleural effusion or pneumothorax is seen . No acute osseous abnormalities are identified .
    OUTPUT:
    
Findings concerning for left lower lobe pneumonia . Followup radiographs after treatment are recommended to ensure resolution of this finding .