Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest provided . The heart is mildly enlarged . The hila appear mildly congested bilaterally . There is no frank pulmonary edema . In the retrocardiac space in the region of the left lower lobe , subtle opacity is noted , difficult to exclude an early pneumonia . No large effusion or pneumothorax . Bony structures appear intact .
    OUTPUT:
    
Mild hilar congestion . Atelectasis versus pneumonia at the left lung base .