Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Since the prior exam , there is slightly increased retrocardiac opacity , suggestive of atelectasis , less likely pneumonia . Otherwise , lungs are clear . Port - A - Cath resides over the left chest wall with catheter tip extending to the low SVC . Cardiomediastinal silhouette is stable . No pneumothorax or effusion . Gaseous distention of colon is noted in the upper abdomen .
    OUTPUT:
    
Subtle streaky left lower lobe opacity likely represents mild increase atelectasis , less likely pneumonia .