The Search is On

Posted by Sara Fazio • February 8th, 2013

In the latest article in our Clinical Problem-Solving series, an 81-year-old man presented to the emergency department with hematochezia and hematemesis, which began after he was awakened by an urgent need to move his bowels. He did not have abdominal pain, black stools, dysphagia, or odynophagia.

An aortoenteric fistula is a communication between the aorta and the gastrointestinal tract. Primary aortoenteric fistulas are extremely rare and most often occur in the presence of an atherosclerotic aortic aneurysm, but they can also be associated with infectious aortitis, enteric ulcers, trauma, tumor, radiation therapy, foreign-body ingestion, and other sources of intraabdominal inflammation (e.g., diverticulitis). Secondary aortoenteric fistulas typically occur in patients with a prosthetic abdominal aortic vascular graft, and are most commonly due to graft infection. Aortoenteric fistulas have also been reported after repair of an endovascular aortic stent.

Clinical Pearls

• How common is an aortoenteric fistula after graft surgery and where do they typically occur?  

The incidence of aortoenteric fistulas after aortic graft surgery is approximately 1 to 3%. The time between aortic repair and fistula formation is usually 3 to 5 years, but fistulas have been reported to occur as early as several days to as long as 20 years after the repair. Aortoenteric fistulas are most commonly located in the distal duodenum, especially the third portion, since the duodenum is fixed and located just anterior to the aorta; however, they can also occur in other areas of the small bowel, colon, stomach, and even the esophagus.

• What is the typical presentation of a patient with an aortoenteric fistula?  

Patients with aortoenteric fistulas classically present with a “herald bleed” consisting of hematochezia, melena, or hematemesis. This episode may spontaneously remit and is followed by more massive bleeding several hours to months later. Some patients, such as the one described here, have repeated episodes of intermittent bleeding. Patients with aortoenteric fistulas can also present with abdominal or low back pain or a pulsatile abdominal mass, as well as fever and bacteremia if they have an associated graft infection.

Morning Report Questions

Q: What should the initial evaluation entail in a patient with a suspected aortoenteric fistula?    

A: The initial evaluation of patients with a suspected aortoenteric fistula should include abdominal imaging and consultation with a vascular surgeon. CT with intravenous administration of contrast material can show evidence of graft infection, such as perigraft soft-tissue thickening or fluid, perigraft or intraluminal gas, thickening of the adjacent bowel wall, loss of tissue planes, disruption of the aneurysmal wrap, pseudoaneurysm, or extravasation of contrast material, or some combination of these findings. When there is a high degree of suspicion for aortoenteric fistula, CT should be performed before other types of gastrointestinal evaluation, since CT can generally be performed promptly, is noninvasive, and is not likely to disrupt a clot and cause further bleeding. Upper endoscopy may be performed to evaluate the distal duodenum, especially the third portion, and to rule out other, more common sources of bleeding. However, endoscopy has a reported sensitivity for aortoenteric fistula of less than 40%, and endoscopic treatment is not possible if a fistula is identified. Tagged red-cell scanning and angiography are rarely helpful in the diagnosis of aortoenteric fistulas, given the intermittent nature of the bleeding.

Q: What is the appropriate treatment in a patient with an aortoenteric fistula?   

A: Patients with untreated aortoenteric fistulas and associated bleeding have a mortality rate of nearly 100%. Surgical repair of secondary aortoenteric fistulas typically involves graft excision and extra-anatomical bypass, which is often complicated and associated with considerable morbidity and mortality. Endovascular techniques have been developed for both temporary and definitive management of aortoenteric fistulas. Observational studies suggest that   endovascular repair, as compared with open surgical repair, is associated with lower rates of postoperative morbidity and mortality but higher long-term risks of infection and recurrent bleeding and may therefore be a better choice in patients with major coexisting conditions or hemodynamic instability.

 

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