Cases of two patients with aortoduodenal fistula who underwent emergency operation

•Aortoduodenal fistula is a rare cause of gastrointestinal bleeding. However, it is life threatening.•Diagnosis requires a high level of clinical suspicion, and surgery can offer the best chance of survival.•Primary aortoduodenal fistula is often caused by aortic aneurysm without any previous vascular intervention.•Secondary aortoduodenal fistula occurs after surgical treatment for abdominal aortic aneurysm.