Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Chest , PA and lateral . There is subtle opacity in the left lower lobe in the setting of low lung volumes , likely atelectasis . The lungs are otherwise underinflated but clear . The cardiac silhouette is minimally enlarged . There is no pneumothorax or pleural effusion . Pulmonary vascularity is normal . An implanted pacemaker is present , with appropriately positioned leads . There is calcification of the thoracic aorta .
    OUTPUT:
    
Left lower lobe atelectasis , less likely pneumonia . .