Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Low lung volumes are present . The heart size is mildly enlarged . Widening of the superior mediastinum is unchanged , and appears attributable to the presence of mediastinal fat as seen on the prior CT . Crowding of the bronchovascular structures is noted , and mild pulmonary vascular congestion is likely present . There is a small left pleural effusion . Retrocardiac opacity persists , and could reflect atelectasis though aspiration or infection can not be excluded . Multilevel degenerative changes are seen within the thoracic spine .
    OUTPUT:
    
Low lung volumes . Mild pulmonary vascular congestion . Small left pleural effusion with persistent left basilar opacity , which could reflect atelectasis though infection or aspiration is not excluded .