Aortoenteric Fistula

Aortoenteric fistula is an abnormal communication between the aorta and the gastrointestinal tract, most often the third or fourth part of the duodenum. It causes massive gastrointestinal hemorrhage and, untreated, is uniformly fatal.

Types

• Primary (very rare, about 0.007 per 100,000 a year): an abdominal aortic aneurysm (usually atherosclerotic) erodes into the duodenum, or infection, tumor or radiation erodes the aorta.
• Secondary (much more common): a complication of aortic graft surgery or endovascular repair, occurring in 0.5 to 2% of open grafts, usually 3 to 5 years after surgery, with higher rates after graft infection.

The bowel sits against the suture line or the graft, and pulsatile pressure with infection causes erosion. The first sign may be a self-limiting herald bleed that precedes catastrophic hemorrhage by hours to months. Mortality is 30 to 40% with treatment, and nearly 100% without. Complications: hemorrhagic shock, sepsis, graft infection and recurrent infection.

• Herald (sentinel) gastrointestinal bleed with hematemesis or melena that stops spontaneously
• Massive hematemesis or hematochezia, hypotension and shock
• Abdominal or back pain, fever and a pulsatile abdominal mass
• Previous aortic graft or aneurysm
• Red flags: any gastrointestinal bleed in a patient with an aortic graft until proven otherwise, fever, and bleeding with a negative upper endoscopy

1. Resuscitation first. Do not delay treatment for investigation in a patient who is unstable.
2. CT angiography of the abdomen and pelvis (sensitivity about 40 to 90%): ectopic gas around the graft, loss of the fat plane between the aorta and the bowel, a pseudoaneurysm, thickened duodenum, and contrast extravasation into the bowel.
3. Upper gastrointestinal endoscopy to the fourth part of the duodenum (a push enteroscope or a longer endoscope), to exclude other causes and to show a graft or clot. Avoid vigorous insufflation.
4. Laboratory tests: full blood count, coagulation, group and cross-match for 10 units, lactate, C-reactive protein, blood cultures and graft cultures at operation.
5. Labeled white cell scan or PET-CT for suspected graft infection in stable patients.

Differentials: peptic ulcer disease, varices, angiodysplasia, mesenteric ischemia, other sources of gastrointestinal bleeding.

1. Resuscitation: two large-bore IV cannulae, massive transfusion protocol (red cells, plasma and platelets in a 1:1:1 ratio), permissive hypotension with a systolic pressure of 70 to 90 mmHg, tranexamic acid 1 g IV over 10 minutes then 1 g over 8 hours, and correction of coagulopathy and hypothermia.
2. Broad-spectrum antibiotics immediately after blood cultures: vancomycin 15 to 20 mg/kg IV every 8 to 12 hours (target trough 15 to 20 mg/L) with piperacillin-tazobactam 4.5 g IV every 6 hours, and fluconazole 400 mg IV daily or an echinocandin (caspofungin 70 mg IV once, then 50 mg IV daily) for suspected fungal infection.
3. Hemorrhage control:
   • Endovascular repair (a stent graft or aortic balloon occlusion) as a bridge in an unstable patient, followed by definitive surgery. It controls bleeding but leaves infection, so antibiotics must continue.
   • Open repair: proximal aortic control, resection of the infected graft or aneurysm, closure of the aortic stump with oversewing, and extra-anatomic revascularization (axillobifemoral bypass) or in situ reconstruction using autologous femoral vein, cryopreserved allograft or rifampicin-soaked graft.
   • Repair the duodenum by primary closure, or resect and reconstruct if necrotic. Drain the retroperitoneum and cover the aortic stump with omentum.
4. Antimicrobial duration: at least 6 weeks of intravenous antibiotics tailored to cultures, followed by long-term oral suppression for 6 to 12 months or for life after endovascular or in situ repair (for example, doxycycline 100 mg orally twice daily or amoxicillin-clavulanate 875/125 mg orally twice daily, depending on organism).
5. Complications: persistent infection, recurrent bleeding, limb ischemia, stump blowout, renal failure, multiple organ dysfunction and death.

Follow-up with CT angiography at 1, 3, 6 and 12 months, then annually, and blood tests (white cell count, C-reactive protein) at each review. Counsel patients with aortic grafts to report any gastrointestinal bleeding, fever or back pain immediately.