Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low , with exaggeration of bronchovascular markings . There is suggestion of a left retrocardiac opacity , which could represent atelectasis or pneumonia . No pleural effusion or pneumothorax . Cardiomediastinal contours are within normal limits . No acute osseous abnormalities identified . A catheter is seen projecting over the upper abdomen on the lateral view , consistent with patient 's ventriculoperitoneal shunt
    OUTPUT:
    
Left lower lobe opacity , may represent atelectasis or pneumonia .