Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is patchy retrocardiac opacity which suggests atelectasis in the left lower lobe , similar to prior findings and seen only on one view . Otherwise , the lungs appear clear . There are no pleural effusions or pneumothorax . Cardiomegaly , as well as mediastinal and hilar contours , appear stable .
    OUTPUT:
    
Persistent patchy left basilar opacity probably due to minor atelectasis , without definite acute disease . Subtle pneumonia is difficult to entirely exclude at the left lung base , however .