Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low resulting in bronchovascular crowding . Opacity within the left lung base is likely a combination of atelectasis and a moderate effusion is slightly increased compared to recent prior . The upper lungs are clear . Cardiomediastinal and hilar contours are unchanged . Right humeral head deformity is unchanged .
    OUTPUT:
    
Progressive left lower lobe opacity , likely ongoing atelectasis and moderate effusion , though underlying pneumonia is possible .