Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP and lateral portable upright chest radiograph obtained . There is basilar atelectasis , more noted along the left lung base . There is no convincing sign of pneumonia though the more localized atelectasis in the left lung base may obscure subtle pneumonia . No large effusion or pneumothorax . No overt signs of CHF . Cardiomediastinal silhouette is normal . Bony structures are intact . Bilateral AC joint arthropathy is noted .
    OUTPUT:
    
Basilar atelectasis , can not exclude subtle pneumonia at the left lung base .