Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP portable upright chest radiograph provided . The left lung base is partially excluded and there is apparent retrocardiac opacity , which could reflect pneumonia . The right lung is clear . No pneumothorax . Bony structures are intact . Overall , cardiomediastinal silhouette appears grossly unchanged .
    OUTPUT:
    
Apparent retrocardiac opacity , which could reflect technique , though pneumonia not excluded . Please confirm with dedicated PA and lateral views as needed .