Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Moderate cardiomegaly , with enlargement of the left atrium , has been stable compared to exams dating back to ___ . The aorta is mildly tortuous , otherwise the hilar and mediastinal contours are unremarkable . A confluent opacity in the retrocardiac region on the lateral view it is difficult to assess in the setting of low lung volumes .
    OUTPUT:
    
Retrocardiac opacity on lateral view is potentially due to crowding of structures in the setting of low lung volumes , but repeat lateral radiograph with improved inspiratory level may be helpful to exclude a an early focus of pneumonia .