Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is mild to moderately enlarged . The mediastinal and hilar contours appear unchanged . A trace pleural effusion is difficult to exclude on the left , none on the right . There is patchy opacity in the right lower lung , probably in the anterior segment of the right lower lobe but not necessarily changed , chronicity unclear .
    OUTPUT:
    
Patchy opacity at the right lung base , not necessarily representing an acute process ; scarring or atelectasis may explain the appearance although pneumonia is hard to exclude .