Answer: Esophageal carcinoma.
The barium swallow shows an irregular stricture with shouldered (overhanging) margins and mucosal destruction in the mid-oesophagus. This is the classic appearance of a proliferative squamous cell carcinoma.
Background: Squamous cell carcinoma and adenocarcinoma are the two commonest oesophageal cancers; SCC favours the mid-oesophagus.
Why not the others: An oesophageal ring (Schatzki) is a thin, smooth, web-like concentric narrowing at the gastro-oesophageal junction. An oesophageal tear shows contrast leak, not a stricture. Achalasia gives a smooth, tapering 'bird-beak' narrowing with a dilated proximal oesophagus, not an irregular shouldered stricture. Ref: Bailey & Love, Short Practice of Surgery, 27th ed, p. 1086