What do you think is causing the upper central abnormality?
There is gaseous distention of the oesophagus, with a gas/fluid level at the level of the carina. This is most likely secondary to oesophageal dysmotility and achalasia.
Could any other conditions give this appearance?
Primary oesophageal disease such as obstruction or Chagas disease could be considered. This is unlikely to be pneumomediastinum due to the distribution of the gas. It would be easy to confuse the line over the right upper lobe for an azygos fissure, until you scrutinise the mediastinal contour.
Distended oesophagus with gas/fluid level at the level of the carina.
Chronic left basal changes. No focal consolidation or lobar collapse.
Normal heart size with normal pulmonary vascularity. Pleural spaces clear.