A 72 year old man presents with intermittent difficulty in swallowing with regurgitation of stale food materials. Sometimes he wakes up at night with a feeling of suffocation. Choose the single most likely cause of dysphagia?

The key is D. Pharyngeal pouch. [In benign stricture, esophageal carcinoma and systemic sclerosis there is persistent dysphagia not intermittent. In oesophageal spasm there may be intermittent dysphagea but there will be no regurgitation of stale food material and no nocturnal regurgitation in recumbency. The clinical picture described well known features of pharyngeal pouch].