Primary AEFs are caused by spontaneous erosion of the aorta into the GI tract. As many as 83% of these cases are associated with abdominal aortic atherosclerotic aneurysms, with a mean diameter of 6.2 cm. Other causes of AEFs include infection (often with tuberculosis or syphilis), cancer, radiation therapy, and foreign body ingestion. Evidence of GI bleeding is observed in 94% of cases, abdominal or back pain is seen in 46% of cases, and a pulsating mass is found in 17% of cases. The classic triad of GI hemorrhage, abdominal pain, and pulsating abdominal mass is present only in 11% of cases.
Classically, AEF initially presents with a minor so-called "herald" bleed, which is followed in hours, days, or weeks by catastrophic hemorrhage. This may be the result of a thrombus providing a tamponade effect on the small fistula, which eventually is dislodged when the fistula expands or is removed at the time of endoscopy (resulting in massive exsanguination directly from the aorta into the small intestine).[1,3,4]
Secondary AEFs are a late complication of aortic graft replacement used to treat aneurysms or aortoiliac occlusive disease. Before 1960, the most common cause of AEFs was aortic aneurysm, followed by infectious aortitis (as mentioned above). Currently, erosion into the intestine by prosthetic vascular grafts has become a common cause, with an incidence of up to 4%. This type of fistula may occur in two different forms:
A graft-enteric fistula (GEF) is a communication between the bowel and the disrupted graft/aorta anastomotic site. Most GEFs develop at the proximal aortic suture line, with the distal duodenum involved in approximately 75% of the cases.
A graft-enteric erosion (GEE) is a breakdown of the enteric wall overlying the graft, resulting in bathing of the graft by enteric contents and chronic graft infection without direct involvement of the suture line (less common).
A 20-year retrospective review of 443 patients with secondary AEFs extrapolated that the mean onset of symptoms after the procedure was 65 months (ranging from 3 days to 27 years) for GEF and 33 months (ranging from 45 days to 5 years) for GEE.
AEF is difficult to diagnose preoperatively because no diagnostic modality with good sensitivity or specificity is available. Patients are usually evaluated by initial upper GI endoscopy, to rule out upper GI bleeding, with a resultant 25% detection rate. Endoscopy should include the entire duodenum because most AEFs occur at the level of the third and fourth portions of the duodenum. In the setting of upper GI bleeding and anemia, bleeding sources from peptic ulcer, postpolypectomy sites, diverticulosis, neoplasm, and angiodysplasia should also be considered in the differential diagnosis.
Clinicians should have a high index of suspicion in EGDs that show no pathologies except for a clot in the duodenum in patients with GI bleeding and a history of previous aortic aneurysm repair or aortobifemoral bypass grafting. Other diagnostic tools include CT scanning with intravenous contrast (61% detection rate) and arteriography (26% detection rate). Only one half of patients with AEF develop positive blood cultures, and one half of those positive cultures yield mixed gram-negative, gram-positive, and fungal organisms.[3,4,7]
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Cite this: Emergency Med Case Challenge: Hemorrhoids, Urinary and Blood Infections in a Woman With Rigors - Medscape - Nov 14, 2022.