A Mysterious Cause of Gastrointestinal Bleeding Disguising Itself as Diverticulosis and Peptic Ulcer Disease: A Review of Diagnostic Modalities for Aortoenteric Fistula

An 81-year-old male with a history of hypertension, hyperlipidemia, smoking, and peptic ulcer disease (PUD) presented with 2 episodes of maroon stools for 3 days and was found to be orthostatic. His PUD was thought to have accounted for a previous upper gastrointestinal (GI) bleed. A colonoscopy revealed 3 polyps and a few diverticuli throughout the colon that were considered to be the source of the bleeding. Two months later, the patient had massive lower GI bleeding and developed hypovolemic shock with a positive bleeding scan in the splenic flexure; however, angiography was negative. A repeat colonoscopy revealed transverse/descending colon diverticular disease and the patient was scheduled for a left hemicolectomy for presumed diverticular bleeding. Intraoperatively, an aortoenteric (AE) fistula secondary to an aorto-bi-iliac bypass graft placed during an abdominal aortic aneurysm (AAA) repair 14 years prior was discovered and was found to be the source of the bleeding. The patient had an AE fistula repair and did well postoperatively without further bleeding. AE fistulas can present with either upper GI or lower GI bleeding, and are universally deadly if left untreated. AE fistulas often present with a herald bleed before life-threatening bleeding. A careful history should always be elicited in patients with risk factors of AAAs such as hypertension, hyperlipidemia and a history of smoking. Strong clinical suspicion in the setting of a scrupulous patient history is the most important factor that allows for the diagnosis of an AE fistula. There are numerous diagnostic modalities for AE fistula, but there is not one specific test that universally diagnoses AE fistulas. Nuclear medicine scans and angiography should not be completely relied on for the diagnosis of AE fistulas or other lower GI bleeds for that manner. Although the conventional paradigm for evaluating lower GI bleeds incorporates nuclear medicine scans and angiography, there is evidence that early endoscopy with enteroscopy may have a better role in severe lower GI bleeding.