Description, Causes and Risk Factors:
Aortoenteric fistula is a rare, life-threatening disease process most commonly a complication of repair of abdominal aortic aneurysms (AAA). It occurs in approximately 0.3-2 % of patients with open AAA repairs.
Although there has been some debate regarding the causative mechanisms of aortoenteric fistula, most observers would agree that either infection or mechanical forces occurring alone or in combination are generally at fault. Once the bowel is open, infection is potentially present even if it was not the initiator of the process.
The exact pathogenesis of the development of aortoenteric fistula has not been fully elucidated, but both mechanical erosion and infection are thought to play a role. Furthermore, recently there have been multiple reports of aortoenteric fistula developing after endovascular aortic repair, despite the theoretical lack of extraluminal disruption. Regardless of etiology, the traditional management goals of aortoenteric fistula have been to control hemorrhage and infection, and maintain adequate distal perfusion. These have been achieved through graft excision and extra-anatomic bypass. In recent years, endovascular repair has emerged as another therapeutic option, particularly for the rapid control of bleeding from aortoenteric fistula.
Primary aortoenteric fistulae are thought to result mostly from direct wear and inflammatory destruction of an aortic aneurysm. Such fistulae, arising from an atherosclerotic abdominal aortic aneurysm, comprise 73% of all primary aortoenteric fistulae, whereas 26% are caused by traumatic or mycotic aneurysms. The most common infectious agents responsible for mycotic aneurysms are Klebsiella and Salmonella, although Staphylococcus and Streptococcus have also been implicated. Much rarer causes, such as radiation, infection, tumors, peptic ulcers, inflammatory bowel disease (Crohn's disease), and ingestion of foreign bodies, account for the remaining 1%. Due to anatomic proximity, the third part of the duodenum is most frequently involved. About two-thirds of primary aortoenteric fistulae occur at this site, whereas the fourth part of the duodenum is affected in one-third of cases.
Secondary aortoenteric fistulae occur as a complication of advanced perigraft infection, an origin that is generally confirmed at either surgery or autopsy. The dominant cause is vascular reconstructive surgery. It has been postulated that a combination of chronic low grade infection of the aortic graft and repetitive pressure on the intestine from aortic pulsations leads to the formation of these fistulas. As a result, aortoenteric fistula and perigraft infection have many similar imaging features.
Primary aortoenteric fistula:
Inflammatory aortitides: Syphilis, tuberculosis, mycotic infection, collagen vascular disease.
Atherosclerotic (Most common in the USA).
Secondary aortoenteric fistula:
Aortic aneurysm repair with prosthetic graft.
Aortic endovascular stent.
Infection of prosthetic aortic graft.
Gastrointestinal disease: peptic ulcer disease, gallstones, pancreatitis, diverticular disease.
Foreign body perforation.
Abdominal aortic aneurysm (AAA).
The clinical signs of aortoenteric fistula include hematemesis, melena, sepsis, acute abdominal pain and vomiting, low blood pressure, rapid heart beat, decreased hemoglobin level, and mild epigastric tenderness.
The three most useful diagnostic modalities for detecting aortoenteric fistulaare abdominal CT scan with intravenous contrast, endoscopy (esophagogastroduodenoscopy), and arteriography. Of these, the CT scan is by far superior as it is less invasive, more convenient, and more expedient than either esophagogastroduodenoscopy or arteriography. CT has another advantage in that it poses no risk of dislodging the aortic thrombus. Because of these qualities, and its widespread availability, short acquisition time, and high resolution, CT has become the first-line modality for imaging evaluation of suspected aortoenteric fistula. However, despite its advantages, CT is of a variable sensitivity and specificity and can miss the presence of an aortoenteric fistula.In very emergent cases when there is no time for pre-angiographic CT, the diagnosis is made by digital subtraction angiography with direct visualization of extravasation of intra-arterial contrast medium by fistula into the bowel lumen.
Esophagogastroduodenoscopy with a water-soluble contrast medium is an excellent investigation to rule out other causes of upper gastrointestinal bleeding such as ulcers and varices. It is helpful in documenting the presence of an aortoenteric fistulaonly when there is leakage of oral contrast material from the disrupted bowel wall into the perigraft space and should be performed only on a hemodynamically stable patient. A negative esophagogastroduodenoscopy does not rule out the possibility of an aortoenteric fistula.
Arteriography has a role in planning aortic reconstruction but, with the great improvements that have taken place in CT imaging, it has a very limited place in the acute setting.Angiography with embolization therapy or stent placement also may be used to treat massive gastrointestinal bleeding secondary to an AEF.
Ultrasonography may be useful in unstable patients or those in whom the use of intravenous iodinated contrast material is contraindicated. However, ultrasonography is rarely indicated for the diagnosis of AEF.
Magnetic resonance imaging requires more acquisition time and greater technical expertise. Pulsation artifacts and the potential inability to differentiate perigraft gas from aortic wall calcification make magnetic resonance imaging of aortoenteric fistulamore difficult.
Conventional treatment of an aortoenteric fistula is surgical. The main goals of operative management are control of hemorrhage and infection, while providing adequate distal perfusion. The definitive surgical treatment consists of closure of the duodenal orifice, aortic ligation to exclude the aneurysm, and an extra-anatomical bypass. In cases of minimal contamination, in situ repair is feasible. These major reconstructive procedures are associated with very high morbidity and mortality.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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