Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Retrocardiac opacity obscuring medial left hemidiaphragm is potentially atelectasis however infectious process can not be excluded . Patient is status post left upper lobectomy with volume loss of the left hemithorax and post surgical changes at the left hilum . Chronic blunting of left costophrenic angle noted . There is no effusion or pneumothorax . The cardiomediastinal silhouette is normal . Left posterior rib changes likely postsurgical . No evidence of free air below the diaphragm .
    OUTPUT:
    
Retrocardiac opacity obscuring medial left hemidiaphragm potentially atelectasis however infectious process can not be excluded . Consider PA and lateral chest radiograph if patient amenable .