What is Aortoenteric Fistula?
An aortoenteric fistula is a rare condition where a connection is formed between the aorta and the digestive tract, which can lead to severe bleeding in the upper digestive system. This condition is very dangerous and can often be fatal. This connection can form in two ways: firstly, it can occur naturally; secondly, it can result from past surgery on the aorta, typically when a synthetic material used during surgery erodes and affects the surrounding digestive system. Symptoms can vary, but the most common sign is intense bleeding in the upper digestive tract, especially in people who have had previous aortic operations or have an aortic aneurysm.
Since patients can deteriorate quickly, quick diagnosis and early repair are critical. Possible treatments include open surgery or an endovascular repair, which is a less strenuous procedure that can serve as a temporary solution before definitive surgery. However, complications after these repairs are usual, and the mortality rate remains high among those who develop an aortoenteric fistula.
What Causes Aortoenteric Fistula?
Aortoenteric fistulas (AEFs) can happen due to either primary or secondary reasons. Primary AEFs form naturally because of direct friction and inflammation in the aorta, which is the main blood vessel in your body. Secondary AEFs, which are more common than primary ones, happen after surgery on the aorta. They typically occur after a synthetic aortic graft material, or a substitute for the aorta, is placed during surgery.
The most common place for an AEF to develop is in the duodenum, especially in its third and fourth segments. The duodenum is the first part of your small intestine and is located very close to the aorta, which makes it a likely place for an AEF to happen.
Risk Factors and Frequency for Aortoenteric Fistula
Aortoenteric fistulas, a rare condition, have been increasingly caused by procedures or surgeries done on the aorta in recent times. These are now more common than the type that happen naturally. The figures show that secondary aortoenteric fistulas occur in 0.36% to 1.6% of patients who receive surgical treatment for their aortic disease. The average age of patients experiencing this condition is 61. Also, the condition is found more frequently in males than in females, which aligns with the higher occurrence and treatment of abdominal aortic aneurysm (a balloon-like bulge in the aorta) in men. To give a clear perspective, for every three to one men to women with primary aortoenteric fistulas, the ratio leaps to eight to one in cases of secondary aortoenteric fistulas.
Signs and Symptoms of Aortoenteric Fistula
Aortoenteric fistulas are serious medical conditions that primarily present as minor or severe bleeding from the gastrointestinal tract, which can sometimes be life-threatening. In some cases, other symptoms such as abdominal pain and the presence of a noticeable mass in the abdomen might accompany the bleeding. But this combination of symptoms is rather rare, being seen in only 6% to 12% of first-time patients.
In comparison, we have aortoenteric erosion — a condition that differs from aortoenteric fistulas by their distinct hemorrhaging behaviors. People with aortoenteric erosion experience chronic intermittent episodes of bleeding, while those with aortoenteric fistulas tend to have massive overt hemorrhages. The most commonly seen symptoms in patients with aortoenteric fistulas are black, tarry stools (melena) and hemorrhagic shock, in addition to abdominal pain and vomiting blood (hematemesis).
Another challenge in diagnosing these conditions comes from the wide-ranging timespan in which secondary aortoenteric fistulas can occur — from as quickly as two weeks after an aortic operation to more than ten years later. So, whenever a patient with a history of aneurysmal disease or aortic surgery experiences gastrointestinal bleeding, doctors should consider the possibility of an aortoenteric fistula. A more prolonged clinical course suggests an aortoenteric erosion, which may also involve recurrent bloodstream infections with bacteria commonly found in the bowels. If this diagnosis is confirmed, it must be assumed that any existing aortic grafts are infected.
Testing for Aortoenteric Fistula
If a patient is in an unstable condition with signs of aortoenteric fistula (AEF), a rare but severe condition, doctors often choose to operate immediately without conducting further tests. If there’s no known history of an abdominal aortic aneurysm (AAA) or previous aorta surgery, a quick ultrasound of the abdomen might be performed to check for aneurysm..
Although an ultrasound can help to identify an AAA, it is not a good tool for diagnosing AEFs due to common issues like bowel gas and intestinal swelling.
In a stable patient with continuous gastrointestinal bleeding, a procedure called upper esophagogastroduodenoscopy (EGD) is often done first. However, it’s not a great tool for diagnosing AEF, as its accuracy is approximately 50% only. Therefore, for these stable patients at high risk for AEF, the initial diagnostic test should be computed tomographic angiography (CTA), which is very precise and sensitive.
CTA is also preferred over a digital subtraction angiography (DSA). In a comparative study, CTA proved to be superior at locating both potential and active bleeding lesions. If the CTA rules out AEF, then it’s appropriate to proceed with an EGD to check for other potential sources of GI bleeding in a stable patient. Colonoscopy is generally not useful for diagnosing AEF, except when symptoms suggest lower GI bleeding, or if a colon-related condition is more likely.
Even with the correct imaging, identifying AEFs can be quite challenging, and often, the diagnosis is not confirmed until an autopsy is performed.
Treatment Options for Aortoenteric Fistula
Treating an AEF (aortoenteric fistula), a complication of surgery that can cause severe bleeding, involves a quick response and a proactive surgical approach. The initial steps involve making sure the patient is stable and ready for surgery which may involve blood transfusions and antibiotics. If the patient’s blood tests show the bacteria Clostridium septicum, doctors will also examine the colon to check for cancer, typically using colonoscopy.
When it comes to the surgical treatment itself, the two main options are traditional open surgery or a less invasive procedure known as endovascular repair of the aorta (EVAR). Both methods come with their respective pros and cons.
Open surgery, for example, seems to result in a lower risk of ongoing infections post-surgery. This is because it allows the surgeon to remove infected tissues and repair the intestinal tract, and in some cases, remove the infected graft. However, open surgery does have a higher in-hospital death rate than EVAR and the patient needs to be strong enough to endure the procedure.
On the other hand, EVAR carries fewer immediate risks and can be particularly useful if the patient has already had multiple surgeries or suffers from a condition like retroperitoneal fibrosis, which makes the abdomen a high-risk area for surgery. The downside of EVAR is that it requires placing graft material into an area that may already be exposed to intestinal contents, which can potentially lead to long-term infections. These infections may warrant long-term use of antibiotics and even further interventions down the line.
When deciding which procedure to follow, if there’s an AEF but no signs of infection, an endovascular repair is usually the first choice. However, if the AEF is secondary or there’s an infection present, endovascular repair can still be used as an initial step to stabilize patients who are not well enough for surgery. Long-term management may include antibiotics and abscess drainage. In some cases, the patient might need another open surgery, while in others, living with a chronically infected graft might be the best choice to avoid strenuous surgery.
To prevent complications like AEF, a one-time ultrasound of the aorta is recommended for all male smokers aged 65 to 75. If diagnosed with an abdominal aortic aneurysm (AAA), they can pursue repair before it develops into an AEF. During open surgical repair of AAA, surgeons should ensure the aortic graft material doesn’t directly touch neighboring structures, especially the duodenum, which can be achieved by wrapping it with a layer of tissue, an omental flap, or a vascularized pedicle.
Lastly, for patients who have had an AEF repair, it’s important to continue regular aortic screening for the rest of their lives.
What else can Aortoenteric Fistula be?
- Transplant infection
- Infected aortic aneurysm (an enlargement of the main blood vessel that can result from a bacterial or fungal infection)
- Infection of the aorta (the main artery in our body)
- Retroperitoneal fibrosis (a condition where fibrous tissue builds up in the back of the abdomen)
- Inflammatory bowel disease (a disorder that causes inflammation in the digestive tract)
- Intestinal tubular adenomas (non-cancerous growths in the gut)
- Angiodysplasia (a condition affecting the blood vessels in the gut)
- Peptic ulcer (a sore in the lining of the stomach or first part of the small intestine)
- Colorectal cancer (a type of cancer starting in the colon or rectum)
What to expect with Aortoenteric Fistula
Despite advancements in imaging and vascular procedures, the survival rate for those who develop an AEF (an abnormal connection between the aorta and duodenum) is still significantly low. For example, in a study of those treated for this condition in the 1980s, only 14% survived, with 36% of patients passing away around the time of their treatment.
Recent studies show slight progress in reducing the mortality rate. One report showed a 50% mortality rate for patients treated for AEF within 60 days of repair, while another report had a slightly lower rate of 43% mortality within 30 days of surgery.
However, it’s important to note that the exact mortality rate for AEF is not fully known. The alarming survival rates shared here only account for those patients who were diagnosed and had surgical repair. Numerous patients pass away before a correct diagnosis can be made, which means they aren’t included in these statistics.
Possible Complications When Diagnosed with Aortoenteric Fistula
There can be quite a few complications that arise due to the formation of an aortoenteric fistulas as well as the treatment linked to it. The most common complications after repairing an AEF are:
- Bleeding shock
- Serious infection resulting in multiple organ failure
- Heart attack and irregular heartbeat
- Aortic stump rupture
- Infection in the graft
- Leaking from the intestine
- Repetitive blood poisoning and severe infection
Preventing Aortoenteric Fistula
An aortoenteric fistula is a condition where part of the wall of the aorta, the main blood vessel in the body, gets worn down and connects with the nearby intestines. When this happens, a large amount of blood can flow into the digestive system, which can cause low blood pressure, vomiting of blood, shock and can even be fatal. The treatment usually involves a major surgical procedure – opening up the abdomen to directly fix the connecting tract, or it can be done endoscopically, which uses a small camera to help doctors see and fix the problem. A small device called an endograft is used to cover the hole in the aortic wall. Despite the treatment options, this condition has a high mortality rate, as many patients pass away before they are diagnosed.
Men aged 65 to 75 who have ever smoked should get a one-time ultrasound of their abdominal aorta to check for the presence of an condition known as an AAA. Moreover, those who have had treatment on their aorta in the past or have had other issues related to the aorta should regularly have check-ups with their vascular surgeon and primary care doctor.
