An aortoenteric fistula (AEF) is an abnormal connection that forms between the aorta, the body’s largest artery, and the gastrointestinal tract. This channel allows blood to leak from the high-pressure circulatory system directly into the digestive system, leading to severe internal bleeding. This condition is considered a surgical emergency that can cause a massive, life-threatening hemorrhage. Without immediate intervention, it is almost always fatal.
Development and Causes of Aortoenteric Fistulas
Aortoenteric fistulas are categorized as either primary or secondary. Primary AEFs are less common and develop when a diseased aorta, such as one with a large abdominal aortic aneurysm (AAA), erodes into an adjacent part of the bowel. This erosion is a slow process driven by constant pressure and inflammation from the aneurysm against the intestinal wall. Conditions like atherosclerosis, which involves the buildup of plaque in arteries, are closely associated with the development of these aneurysms.
Secondary AEFs are more common and arise as a complication of previous aortic surgery, often months or years after the placement of a synthetic graft. A low-grade infection of the graft material can gradually weaken the tissue, allowing the graft to erode into the nearby bowel. The duodenum is the most commonly affected section.
A fistula can also form from mechanical factors, where the prosthetic graft rubs against the bowel over time, causing friction that wears through both structures. Risk factors for a secondary AEF include a history of aortic surgery, graft infection, and situations where the graft is in direct contact with the bowel without a sufficient tissue barrier.
Recognizing the Symptoms
The signs of an aortoenteric fistula can be subtle. A key indicator is a “herald bleed,” which involves smaller episodes of gastrointestinal bleeding that may stop on their own. These episodes can manifest as vomiting blood or dark, tarry stools and may occur weeks before a massive hemorrhage. This initial bleed is caused by a temporary clot forming within the fistula.
The classic triad of symptoms includes gastrointestinal bleeding, abdominal pain, and a palpable, pulsating abdominal mass, but it is rare for a patient to have all three. Abdominal or back pain is a common symptom, resulting from the aneurysm or inflammation around the fistula. If the underlying cause is an aortic graft infection, systemic symptoms may be present.
Patients may also experience signs of infection like fever, chills, and unexplained weight loss. Significant blood loss leads to signs of hemorrhagic shock, including low blood pressure, a rapid heart rate, dizziness, and confusion. Any gastrointestinal bleeding in a person with a history of an aortic aneurysm or prior aortic surgery should raise suspicion for an AEF.
The Diagnostic Process
Diagnosing an aortoenteric fistula is challenging because its symptoms mimic more common causes of gastrointestinal bleeding. The most effective diagnostic tool is a computed tomography angiography (CTA) scan of the abdomen and pelvis. This specialized imaging provides detailed cross-sectional views of the blood vessels and surrounding structures.
On a CTA scan, radiologists look for specific signs that suggest a fistula. These signs can include:
- The presence of air or fluid collections around the aortic graft, which is not normally present
- Visible leakage of contrast dye from the aorta directly into the lumen of the bowel
- A loss of the normal fat plane that separates the aorta from the intestine
- Thickening of the adjacent bowel wall
While CTA is the primary imaging modality, an upper endoscopy, or esophagogastroduodenoscopy (EGD), is often performed to rule out other sources of upper GI bleeding, such as ulcers. This procedure involves inserting a flexible camera through the mouth to examine the esophagus, stomach, and the first part of the small intestine (duodenum). In some unstable patients, the diagnosis is only confirmed during emergency surgery.
Surgical and Medical Management
Treatment for an AEF is a surgical emergency focused on controlling hemorrhage, repairing the aorta and bowel, and eradicating infection. The definitive approach is open surgical repair. This involves removing the infected aortic graft, repairing the hole in the intestine, and restoring blood flow to the lower body.
To avoid placing a new graft in an infected area, surgeons perform an extra-anatomic bypass. This routes a new graft through uninfected tissues, connecting a healthy artery above the infection to the femoral arteries in the legs. The section of intestine involved in the fistula is also surgically closed or removed.
A less invasive option, endovascular repair, may be used in certain situations. This technique involves deploying a stent-graft inside the aorta to cover the fistula opening from within. This can rapidly control bleeding and is often used as a temporary “bridge” to stabilize a patient before a major open operation. However, endovascular repair alone does not address the infected tissue.
Long-term management of the infection is a primary part of treatment. Patients require a prolonged course of targeted antibiotics, sometimes for life. The specific antibiotics are chosen based on cultures taken from infected tissue during surgery to ensure they are effective against the bacteria involved.