Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Mild cardiomegaly has been stable compared to exams dated back to at least ___ . The hilar and mediastinal contours are normal . Subtle increase in opacification at the right lung base is unexplained . There is a small right pleural effusion . No evidence of pneumothorax . The visualized osseous structures are unremarkable .
    OUTPUT:
    
No acute intrathoracic abnormalities identified .