Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a subtle focal opacity seen only on the frontal view , relatively rectangular in shape , projecting over the anterolateral left sixth rib , which may be due to prior rib injury or may be external to the patient . Correlate with history . Shallow oblique radiographs would help further assess . Otherwise , no focal consolidation is seen . An azygos lobe is incidentally noted . No pleural effusion or pneumothorax is seen . The cardiac and mediastinal silhouettes are unremarkable .
    OUTPUT:
    
Subtle focal opacity , relatively rectangular in shape , projecting over the anterolateral left sixth rib , which may be due to prior rib injury or may be external to the patient . Correlate with history . Shallow oblique radiographs would help further assess .