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Management of Primary Aortoenteric Fistulas
Fistulas between major vascular structures and the intestinal tract are grouped into two categories: primary and secondary. A primary aortoenteric fistula is an abnormal spontaneous communication between the aorta and a segment of the alimentary tract without any history of previous aortic operation. A secondary aortoenteric fistula is caused by the erosion of a component of a previous vascular reconstruction, usually a prosthetic graft into a nearby portion of the intestinal tract.
Primary aortoenteric fistulas are extremely rare. In a large autopsy series the incidence was found to be 0.04% to 0.07%. The incidence is increased in patients with an abdominal aortic aneurysm (AAA), being between 0.69% and 2.36%. As with AAAs, there exists a male-to-female preponderance of 3:1with primary aortoenteric fistulas.
An aortoenteric fistula was initially described by Sir Astley Cooper in 1829. The first successful repair was performed in 1958 by Herberer in Germany using an aneurysmorrhaphy technique. Few advances were made in treatment until 1987, when the benefits of a staged repair were presented (i.e., extra-anatomic bypass followed by repair of the fistula and aortic excision). Recent studies have advocated the use of a variety of arterial conduits for in situ repair, and even more recently endovascular techniques have provided another option in the treatment of these lesions.
Etiology
All portions of the gastrointestinal tract, including the appendix, have been involved in primary aortoenteric fistulas, but up to 80% occur between the aorta and the third and fourth portions of the duodenum. This is thought to occur because of the relatively fixed position of the duodenum in the retroperitoneum and its anatomic proximity to the anterior surface of the aorta. The esophagus is the second most common site of primary aortoenteric fistula formation, accounting for 28% of cases in one review. Historically, before the availability of antibiotics, primary aortoenteric fistulas were associated with certain infectious states including syphilis, tuberculosis, and other infected aneurysms. Currently more than two thirds are related to the common type of degenerative aneurysms. Several cases have been reported following endovascular aneurysm repair because of endoleaks or endotension (some authors consider these to be secondary because an aortic operation has been performed).
The pathophysiology of fistula formation is thought to be related to mechanical erosion of the pulsatile aorta into surrounding adherent structures, in combination with a local inflammatory process. Other even rarer causes have been reported in the literature, including appendicitis, carcinoma, cholelithiasis, diverticulitis, radiation therapy, peptic ulcer disease, trauma, and foreign body perforation of the intestinal tract. Perforation has been reported in young children who have swallowed chicken or fish bones.
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