Aortoenteric Fistula (AEF): Symptoms, Diagnosis, And Treatment

a "fistula" is a communication between any two body parts, usually two hollow or tubular structures in the body, most commonly caused by some kind of pathologic process. "Enteric" means related to the inside of the bowels. An aortoenteric fistula (AEF) is, therefore, defined as a pathologic communication between the aorta and the gastrointestinal (GI) tract.

There are two main types of aortoenteric fistulae

1. Primary AEF

Primary AEF is extremely rare. In this condition, a native (previously unoperated) chronic aortic aneurysm communicates with the digestive tract, most commonly the duodenum, because it’s usually positioned near the aorta. Other than the duodenum, primary AEF can also communicate with the esophagus, small and large bowel, and rarely, the stomach. It’s three times more common in older men, with the average aortic diameter measuring more than 6 cm.

The aneurysm slowly destroys both the weakened aortic and the duodenum tissue, eventually eroding its walls, and forming the fistula. The majority of AEFs are caused by some sort of infection, although other reasons, such as GI tract diseases, tumors, foreign bodies, and radiotherapy, can also trigger this process.

2. Secondary AEF

Secondary AEF is linked with prior aortic repair surgery (prosthetic graft replacement), with symptoms generally starting few years after the procedure. In this case, the graft communicates with the digestive tract, most commonly between the end of duodenum and the beginning of the small bowel, but it ultimately depends on the location of the graft itself.

What are the symptoms of AEF?

Patients with AEF have a characteristic triad of symptoms:

• Gastrointestinal bleeding, manifested as bloody stool, which can be minimal and self-limited due to blood clot formation (herald bleed), but also massive and dramatic
• Abdominal pain
• Pulsatile abdominal mass

However, only a small percent of patients shows all of the symptoms at the same time. Other symptoms may include fever, back pain, and sepsis. Blood vomiting, increased heart rate followed by low blood pressure, and low hemoglobin may also be present.

How is AEF diagnosed?

The most commonly used method in AEF diagnosis is the CT scan with contrast agent applied, because other than being non-invasive, it can help by visualizing the issue using 3D reconstruction, and thereby help in planning the procedure. Other imaging tests involve abdominal X-ray, MRI, and aortography.

Gastroduodenoscopy (a procedure where a long, flexible plastic tube with a camera on top in inserted into the GI tract via the mouth) is also used, primarily because it helps in visualizing the problem first-hand, but because it’s generally uncomfortable for the patients, and may take relatively long, it is not used as much as the CT scan.

Can AEF be treated?

Surgery is the only effective method in treating AEF.  Conservative methods, such as medication therapy without operation, are fatal. Prior to the procedure, the surgeon must be informed of several things:

• Is there any active bleeding?
• Is the AEF primary or secondary?
• Is sepsis present?
• What is the condition of the patient’s aorta (aneurysms, occlusion)?

With this in mind, the surgeon’s first goal is to get any active bleeding under control, usually by clamping the aorta or by using special balloon catheters. The next step would be to separate the bowel from the aorta, and finally reconstructing and closing both parts.

In secondary AEF, the surgeon must remove all infected tissues, and then repair the defects in both the bowel and the missing part of the graft. If the situation allows for it, the graft can be completely replaced, and even an EVAR procedure may be an option. Before, as well as after the surgery, an antibiotic therapy is prescribed, lasting up to six weeks, and even lifelong in the case EVAR was performed.

Due to the complicated nature of both the AEF and the surgery, the mortality rate is still relatively high. Roughly one third of patients die. However, a modern surgical approach has shown fewer complications than before, reducing the amputation rate to less than 10 percent.