Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A portable upright radiograph of the chest demonstrates markedly low lung volumes . There is a retrocardiac opacity . The right lung and left upper lung are clear . There is no pneumothorax . There is a possible left pleural effusion . Top normal heart size is unchanged . Pulmonary vascularity is normal .
    OUTPUT:
    
Low lung volumes makes evaluation limited . However , there is left retrocardiac opacity which may be technical but can not exclude subtle aspiration . Correlate clinically .