List six causes of gastric outlet obstruction.

1. Benign stricture (e.g., as a result of acute or chronic peptic ulcer disease)
2. Invasion of the stomach by pancreatic or colon cancer
3. Gastric neoplasm
4. Metastasis
5. Crohn’s disease of the stomach
6. Prior vagotomy or partial gastrectomy with anastomotic ulcer or bezoar