Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a large left - sided pleural effusion causing significant compressive atelectasis . The upper left lung and right lung are grossly clear . The cardiac size is difficult to evaluate given the large pleural effusion .
    OUTPUT:
    
Large left pleural effusion with adjacent substantial left lung atelectasis . Potential etiologies of a large pleural effusion include malignancy , infection , and , in the appropriate clinical setting , a hemothorax .