Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to prior , there is new moderate left basal atelectasis with associated leftward shift due to volume a loss and small left pleural effusion . The evaluation of left heart border is difficult , but the heart size is likely normal . Mediastinal and hilar contours are unremarkable . The right lung is clear . There is no pneumothorax .
    OUTPUT:
    
Interval development of small left pleural effusion and moderate left basilar atelectasis since ___ .