Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is mildly enlarged . There is calcification of the aortic knob . The mediastinal and hilar contours are stable . Increased opacity at the right lung base likely reflects a moderate sized pleural effusion . However , an underlying infectious process can not be excluded . The upper lungs are essentially clear . There is no definite pneumothorax .
    OUTPUT:
    
Moderate right pleural effusion , an underlying infectious process however can not be excluded .