Abstract
We present a patient with gastrointestinal bleeding secondary to an aortoduodenal fistula. The patient had undergone an open surgical repair of an abdominal aortic aneurysm five years prior to admission.
Introduction
Aortoenteric fistula (AEF) is an uncommon but life-threatening complication of aortic reconstructive surgery. In the past, the most common cause of abdominal aortoenteric fistulas was aortic aneurysm, followed by infectious aortitis due to syphilis or tuberculosis, but currently intestinal erosion by prosthetic vascular grafts has become a much more common cause, with an incidence of up to 4%. [1] Without surgical intervention, AEF has a mortality rate of nearly 100%. The usual imaging modalities available include angiography and contrast-enhanced computed tomography (CT). Of these, CT is the non-invasive test of choice. Here, we are presenting a patient with gastrointestinal bleeding secondary to aortoduodenal fistula who had undergone an open surgical repair of an abdominal aortic aneurysm 5 years prior to this admission.
Case
A 79-year-old man with a past surgical history of an open repair of an abdominal aortic aneurysm in 2000, and a past medical history of emphysema and asbestosis, was admitted to our hospital with progressive weakness, dizziness, melena, and epigastric pain for one week. On the day of admission, he had an episode of syncope. In the emergency department he was found to be hypotensive and anemic. Gastric lavage was positive for hemorrhage, and subsequent endoscopy showed hemorrhage in the distal duodenum. A CT was performed of the abdomen and pelvis, without oral or IV contrast (the latter because the patient's serum creatinine was elevated). This demonstrated gas in the wall of the aortic graft and diffuse proximal to mid small bowel intraluminal hemorrhage (Fig. 1). The patient was taken emergently to the operating room for exploratory laparotomy, and an intra-operative angiogram was performed, which further confirmed the aortoenteric fistula (AEF). Surgical and pathological findings were those of an aortoduodenal fistula with an infected aortic graft. The patient survived repair with excision of the graft and axillary-bifemoral bypass.
CT scan of the abdomen without oral or IV contrast shows gas in the anterior wall of the aortic graft (short arrow), and diffuse high density luminal contents in the small bowel (large arrows) representing hemorrhage. These findings are diagnostic of aortoenteric fistula, in a patient with aortic aneurysm repair several years earlier.
Discussion
Aortoduodenal fistula has been reported to occur in 0.2 to 4% of patients who have undergone aortic reconstruction [2]. Erosion into the intestine by a prosthetic vascular graft, although very uncommon, is much more common than primary aortoenteric fistula, where the patient has not had previous surgery [3]. AEF has even been reported following endovascular repair (i.e. stent-graft placement) of abdominal aortic aneurysms. Aortoenteric fistula and graft infection go hand-in-hand. The 20-year experience with secondary AEF at Johns Hopkins showed the average interval between initial surgery and presentation to be 2.8 years [4]. Seventy percent or more of patients with a communication between an aortic graft and the duodenum present with gastrointestinal bleeding, most classically a combination of upper and lower bleeding, as the location of the fistula is usually near the ligament of Treitz. Urgent diagnosis and treatment are necessary, since the mortality of untreated AEF within the first 24 hours is up to 46%. The initial presentation, however, may be subacute, and the patients may present with an initial “herald” bleed, which is the result of a small fistula which is tamponaded by thrombus formation [5]. AEFs involve the third and fourth portions of the duodenum (88%), and less often the more proximal duodenum (8%), the jejunum, or the ileum [6]. The sensitivity and specificity of CT for the detection of AEF has not been prospectively studied to our knowledge. Two older studies retrospectively compared the CT findings with the subsequent operative results, and concluded that CT is 94% sensitive and 85% specific for the diagnosis of AEF [7]. Despite these findings, a high clinical and radiographic index of suspicion should always be maintained in a patient with prior abdominal aortic repair and otherwise unexplained GI bleeding. In AEF, CT may demonstrate gas or fluid around the graft, which should not be present beyond the immediate peri-operative period, as well as pseudoaneurysm formation. CT angiography is now prefered to conventional angiography in suspected AEF because one can see the aortic lumen, the aortic/graft wall, look for subtle gas, assess extra-vascular/adjacent collections, look at the duodenum/jejunum, and assess for active contrast extravasation. Conventional angiography cannot permit this degree of assessment. There are essentially no prospective studies and few retrospective studies comparing imaging modalities, because this condition is unusual and patients are not typically stable enough to undergo enrollment in trials/undergo multi-modality evaluation. Our patient had a diagnostic CT, even without IV contrast. The intraoperative angiogram in our patient was used for surgical planning and may not be needed in most patients. Upper endoscopy may demonstrate the actual communication between the third or fourth portions of the duodenum and the aorta, but more frequently shows hemorrhage and other signs indicative of the fistula. Alternatively, other explanations for the gastrointestinal hemorrhage can be demonstrated on endoscopy. Treatment of AEF usually consists of graft excision, closure of the duodenal defect, retroperitoneal debridement, and extra-anatomic bypass. Recently, stent-grafting has been utilized for the treatment of ruptured and nonruptured aortic aneurysms, traumatic aortic injuries, and various fistulas involving the aorta [8]-[12]. This minimally invasive approach has the potential to overcome the problems encountered with standard open repair and is particularly attractive in high-risk patients and emergent situations. Infections involving endovascular prostheses have been reported and can be quite severe, ultimately requiring removal of the device and conventional graft reconstruction.