Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low which accentuates the cardiomediastinal silhouette . The cardiomediastinal silhouette is top normal in size . There is a retrocardiac opacity with obscuration of the left hemidiaphragm . The right lung is grossly clear . There is no large pleural effusion or pneumothorax . Median sternotomy wire and mitral valve replacement are unchanged in appearance . Calcification is noted in the descending aorta . Degenerative changes are noted about the acromioclavicular joints bilaterally . There is no definite rib fracture identified .
    OUTPUT:
    
Retrocardiac opacity with obscuration of the left hemidiaphragm could represent atelectasis or left lower lobe pneumonia in the correct clinical setting .