Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear unchanged . A pigtail drainage catheter has been placed in the lower left pleural space . The large majority of a loculated pleural effusion has been drained with a moderate residual quantity and parenchymal opacity which can probably be attributable to atelectasis , although an infectious etiology is not excluded by this study . Elsewhere , the lungs remain clear . A small pleural effusion on the right is unchanged . There is no pneumothorax .
    OUTPUT:
    
Marked improvement in left pleural effusion following placement of catheter .