Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A left - sided chest tube terminates within the left lung apex . There is persistent opacification of the left lung base likely related to atelectasis . Overall , aeration of the left lung base appears slightly improved . Linear opacities within the lower left lung are likely related to areas of subsegmental atelectasis . No large pleural effusion is identified . The right lung is clear . No residual pneumothorax is evident . There is no vascular congestion or edema . Visualized cardiomediastinal contours are within normal limits . Subcutaneous air along the left chest wall appears similar to prior and is likely related to prior placement of a chest drain .
    OUTPUT:
    
1 . Left chest tube in standard expected position . No residual pneumothorax . 2 . Slight improved aeration of the left lung base with persistent probable retrocardiac atelectasis .