Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest were obtained . Lung volumes are significantly lower than on the prior study , resulting in bronchovascular crowding . Opacity at the left lung base is likely combination of tiny effusion and atelectasis but supervening infection can not be excluded . The upper lung zones are clear . No pneumothorax and no right pleural effusion . Pulmonary vasculature is normal . Cardiac and mediastinal silhouettes are stable allowing for lung volumes . An abdominal drain projects over the left upper quadrant . Clips are seen in the thyroid bed after total thyroidectomy .
    OUTPUT:
    
Left basilar opacity is likely a small effusion and atelectasis but supervening pneumonia can not be excluded . No edema .