Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Low lung volumes accentuate the cardiomediastinal silhouette , however mild cardiomegaly has slightly increased in size compared to the prior exam from ___ . There is mild pulmonary vascular congestion otherwise the hilar and mediastinal contours are normal . There is a retrocardiac opacity with obscuration of the left hemidiaphragm . Median sternotomy wires and mitral valve replacement are unchanged in appearance . Calcification is noted in the descending aorta . Degenerative changes are seen in the acromioclavicular joints bilaterally .
    OUTPUT:
    
1 . Retrocardiac opacity with obscuration of left hemidiaphragm may be secondary to atelectasis , however left lower lobe pneumonia can not be excluded . 2 . Mild pulmonary vascular congestion .