Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . There is a left basilar opacity and retrocardiac density , concerning for lower lobe pneumonia or effusion . Linear opacities at the right base likely reflect atelectasis . The remaining areas of the lungs are clear . The central pulmonary vessels are prominent . There is no pneumothorax or large pleural effusion . The left costophrenic angle is excluded from the study .
    OUTPUT:
    
Left lower lobe pneumonia or effusion . A lateral radiograph can be obtained to further localize this process .