Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are low . The cardiac , mediastinal and hilar contours appear unchanged . There is no pleural effusion or pneumothorax . Opacification lying posterior to the left hemidiaphragm is non-specific ; noting low lung volumes , opacity could potentially be seen with atelectasis , but may reflect bronchopneumonia , best seen on the lateral view .
    OUTPUT:
    
Left posterior basilar opacity , possibly pneumonia .