Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post sternotomy . The heart is moderately enlarged . Projecting over the mid chest , and seen only on the frontal view , is an irregular air collection projecting below the level of the carina . Otherwise , the mediastinal and hilar contours appear unchanged . There is no pleural effusion or pneumothorax . Mild loss in lower vertebral body heights appears unchanged . The bones may be demineralized to some degree .
    OUTPUT:
    
Irregular air collection projecting over the central lower mediastinum , probably referring to the esophagus ; the etiology is uncertain . There are variety of possibilities including esophageal pathology , including the possibility of perforation , although dilatation due to dysmotility or inflammation of the esophagus may explain the appearance .