Aortoenteric fistulae are pathologic communications between the aorta (or aortoiliac tree) and the gastrointestinal tract and represent an uncommon cause of catastrophic gastrointestinal hemorrhage.
Aortic fistulae may be considered primary (associated with a complicated abdominal aortic aneurysm) or secondary (associated with graft repair).
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Epidemiology
The annual incidence of primary aortoenteric fistulae is thought to be around 0.007 per million while that of secondary aortoenteric fistulae is about ~1% (range 0.6-2%) 1.
The incidence of secondary aortoenteric fistulae is found to be higher in patients following open aortic repair compared to patients with endovascular stent placement.
Clinical presentation
classically, a aortoenteric fistula may initially present with minor "herald" gastrointestinal hemorrhage, followed by a later catastrophic life-threatening gastrointestinal hemorrhage
primary aortoenteric fistula may present with recurrent septicemia with enteric pathogens
Pathology
A primary aortoenteric fistula forms when a large abdominal aortic aneurysm or a penetrating aortic ulcer 1 closely abuts bowel loops, usually the 3rd or 4th parts of the duodenum. Similarly, in the chest, when a large thoracic aortic aneurysm compresses the esophagus. Due to long-standing pressure, the aneurysm slowly erodes into the bowel or esophageal wall. These are most commonly due to infected mycotic aneurysms.
Secondary aortoenteric fistulae are seen as a complication of aortic reconstructive surgery with or without the placement of an aortic stent-graft. Secondary fistulae that result from perigraft infection may occur between 2 weeks and 10 years after surgery.
Radiographic features
CT
Primary aortoenteric fistula
Direct signs include:
ectopic gas adjacent to or within the aorta
presence of vascular contrast within the gastrointestinal tract
Indirect signs include:
bowel/esophageal wall thickening overlying an aneurysm
disruption of the aortic fat cover
retroperitoneal/mediastinal hematoma or hematoma within the bowel wall or lumen
Secondary aortoenteric fistula
increased perigraft soft tissue
pseudoaneurysm formation
disruption of aneurysmal wrap
increased soft tissue between the graft and aneurysmal wrap
Treatment and prognosis
The only curative treatment is surgery. Without prompt surgical intervention, mortality approaches 100%. Operative mortality itself is as high as 50%.
Differential diagnosis
On imaging, consider:
perigraft infection without fistulisation
History and etymology
First described by Sir Astley Cooper (1768-1841), a British surgeon in the early 19th century 6.
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