Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared with prior radiographs on ___ , again seen are low lung volumes , with a retrocardiac opacity and obscuration of the left hemidiaphragm . There is a small left pleural effusion with blunting of the costophrenic angle . Right basilar atelectasis is unchanged from prior . There is equivocal vascular congestion , no pulmonary edema . The cardiomediastinal silhouette is unchanged .
    OUTPUT:
    
Left lower lobe opacity with low lung volumes may represent atelectasis , however in the appropriate clinical setting , pneumonia is a possibility .