Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP portable upright view of the chest . A prominent retrocardiac opacity corresponds with known hiatal hernia . Lung volumes are low with mild bibasilar atelectasis . The cardiac silhouette appears unchanged . Mediastinal contour is within normal limits . There is no convincing evidence of pneumonia , edema , large effusion or pneumothorax . The imaged osseous structures are intact . No free air below the right hemidiaphragm .
    OUTPUT:
    
Large hiatal hernia . Mild bibasilar atelectasis , otherwise unremarkable exam .