Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Linear opacity within the left lung base may be due to subsegmental atelectasis , though focal pneumonia is possible in the appropriate clinical setting . . No overt interstitial edema is identified . Mediastinal and hilar contours are within normal limits . There is mild cardiomegaly . No pneumothorax is identified .
    OUTPUT:
    
Left basilar opacity , possible atelectasis , though pneumonia should be considered in the appropriate clinical setting .