Aortoenteric fistula (AEF) is an abnormal communication between the aorta and the gastrointestinal tract (most commonly the 3rd or 4th portion of the duodenum). Two types exist: primary AEF (from atherosclerotic aneurysm, infection, or tumor erosion — rare) and secondary AEF (after previous aortic surgery or endovascular graft — much more common with 0.5-2.3% incidence). Secondary AEF typically develops from chronic mechanical irritation and low-grade infection between the graft and the 3rd portion of the duodenum after aortobifemoral bypass or EVAR. It presents with massive gastrointestinal bleeding (hematemesis and/or melena) — a 'herald bleed' followed by massive hemorrhage is the classic presentation. On CTA, periaortic/perigraft gas bubbles, loss of fat plane between aorta and bowel, direct contact between aneurysm/graft and bowel wall, and contrast leakage into bowel lumen are the main findings. Untreated, it is 100% fatal; emergent surgical graft removal and extra-anatomic bypass is required.
Age Range
50-80
Peak Age
65
Gender
Male predominant
Prevalence
Rare
In primary AEF, chronic inflammation and pulsatile mechanical stress in the atherosclerotic aneurysm wall progressively erode the adjacent duodenal wall. As the aneurysm expands, the 3rd portion of the duodenum (retroperitoneal, fixed anterior to the aorta) is compressed and ischemic pressure necrosis develops → a fistula forms between the aortic and bowel walls. In secondary AEF, chronic mechanical contact between the synthetic graft (Dacron or PTFE) and duodenum, transmission of graft pulsation to the bowel wall, and low-grade perigraft infection through biofilm formation together lead to fistula development. The graft material cannot vascularize (it is not biological tissue) → an avitalized zone prone to bacterial colonization remains at the graft-tissue interface. On CT, periaortic gas bubbles reflect anaerobic bacterial gas production from this low-grade infection — gas creates dramatic contrast against surrounding tissue at -1000 HU on CT. Loss of fat plane indicates inflammatory obliteration of normal fat tissue between the aorta/graft and bowel wall. During active bleeding, contrast leaks into the bowel lumen because high-pressure arterial blood flows through the fistula tract into the low-pressure bowel lumen.
Presence of small gas bubbles (-1000 HU) around the aorta or synthetic graft. Without recent surgical history, this finding strongly suggests anaerobic infection and aortoenteric fistula. Gas reflects intestinal gas passing through the fistula tract into the periaortic space or gas produced by anaerobic bacteria.
Small gas bubbles (-1000 HU) around the aorta or synthetic graft on CTA. This finding indicates periaortic/perigraft infection and anaerobic bacterial activity. In the absence of recent surgical history (<4-6 weeks), periaortic gas should raise high suspicion for AEF or graft infection. In the early postoperative period, small amounts of perigraft gas may be normal, but persistent or increasing gas is pathological. Gas quantity and distribution reflect the extent of infection.
Report Sentence
Ectopic gas bubbles around the aorta/graft, consistent with perigraft infection and/or aortoenteric fistula.
Loss of the normal retroperitoneal fat plane between the aorta or graft and duodenum (usually 3rd portion) on CTA. Normally, 2-5 mm thick fat tissue (-80 to -120 HU) exists between the aorta and duodenum. In fistula development, inflammatory granulation tissue and fibrosis completely obliterate this fat plane → the aorta/graft and bowel wall come into direct contact. This is the most sensitive but limited specificity finding in AEF diagnosis — postoperative fibrosis and radiation can also cause fat plane loss.
Report Sentence
Loss of the retroperitoneal fat plane between the aorta/graft and duodenum, raising suspicion for aortoenteric fistula.
Active contrast extravasation into the duodenal lumen on CTA — contrast passes from the aortic lumen through the fistula tract into the bowel lumen. This finding is definitive evidence of active bleeding and constitutes an emergent surgical indication. Intraluminal contrast (200-300 HU) is markedly denser than surrounding bowel content (0-30 HU). On delayed phase, contrast progression along the bowel may be seen. During the herald bleed period, bleeding is intermittent and may not be visible on the initial CTA.
Report Sentence
Active contrast extravasation into the duodenal lumen, evidence of active bleeding consistent with aortoenteric fistula; emergent surgical intervention is required.
Fluid or soft tissue density collection around the graft. In the normal postoperative period (first 6-8 weeks), minimal perigraft fluid may be present, but in the late period (>3 months), perigraft fluid is pathological and suggests graft infection. Fluid density reflects the stage of graft infection — low density (transudate), high density (hematoma/pus). If gas bubbles accompany, infection is certain. PET-CT with perigraft FDG uptake can confirm infection activity.
Report Sentence
Perigraft fluid collection noted, to be evaluated for perigraft infection and possible aortoenteric fistula.
Perigraft collection or tissue thickening showing T2 hyperintense signal on MRI. T2 hyperintensity reflects high water content — inflammatory exudate, edema, or abscess. Perigraft collection showing DWI restriction is strong evidence for abscess. Perigraft rim enhancement on contrast-enhanced sequences indicates inflammatory capsule. MRI is used in addition to CTA for assessment of infection extent and tissue characterization.
Report Sentence
Perigraft collection/tissue thickening showing T2 hyperintense signal, consistent with perigraft infection.
On Doppler US, perigraft fluid collection and/or arterial flow signal may be detected around the graft. Perigraft collection appears hypoechoic to mixed echogenic on B-mode. Unexpected arterial flow around the graft on color Doppler may indicate fistula tract leak flow from AEF or pseudoaneurysm formation. US sensitivity is lower than CTA but can be used for bedside evaluation and follow-up.
Report Sentence
Perigraft fluid collection and arterial flow signal on Doppler around the graft, further evaluation with CTA recommended for perigraft pathology.
Criteria
Develops without prior aortic surgery or endovascular intervention history. Occurs in the setting of atherosclerotic aneurysm, infection (mycotic aneurysm), radiotherapy, or tumor erosion. Very rare (0.04-0.07% prevalence).
Distinct Features
Usually associated with large AAA involving the 3rd portion of duodenum. No graft present — periaortic gas less frequent. Fat plane loss and aneurysm wall-bowel contact area are more prominent.
Criteria
Develops after previous aortic surgery (aortobifemoral bypass, tube graft) or endovascular intervention (EVAR). Incidence 0.5-2.3%. Median latency period 3-5 years but can occur years to decades later.
Distinct Features
Perigraft gas and fluid collections more common. Graft-bowel contact point usually at proximal anastomosis. Biofilm and chronic low-grade infection play central role in pathogenesis.
Criteria
The graft does not directly open into the bowel lumen but erosion and inflammatory contact exist between graft and bowel wall. Considered an early/incomplete form of graft-enteric fistula.
Distinct Features
Active contrast leakage into bowel lumen may not be present. Presents with perigraft inflammation, fat plane loss, and minimal gas findings. Bleeding is usually less massive, may be intermittent (herald bleed).
Distinguishing Feature
In aortic rupture, bleeding is directed into the retroperitoneal space or peritoneal cavity without direct bowel communication. No periaortic gas. Draped aorta sign and retroperitoneal hematoma are prominent.
Distinguishing Feature
Mycotic aneurysm may show saccular morphology, periaortic soft tissue and gas, but no direct bowel communication or contrast leakage into bowel lumen. Aneurysm is usually at atypical location (non-aneurysmal aortic segment).
Distinguishing Feature
In endoleak, contrast accumulates outside the graft but within the aneurysm sac, no bowel communication. Periaortic gas and fat plane loss are not seen in endoleak.
Distinguishing Feature
In isolated graft infection, perigraft fluid and gas may be present but no contrast leakage into bowel lumen and no direct anatomic communication with bowel can be demonstrated.
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAEF is 100% fatal without treatment. AEF should be considered in the differential diagnosis of every patient presenting with massive GI bleeding (especially with aortic surgery history). 'Herald bleed' — initial minor bleeding episode followed by massive hemorrhage — is the classic presentation and offers an opportunity for early diagnosis. Treatment is emergent surgery: infected graft removal, debridement, and extra-anatomic bypass (axillofemoral bypass) or in-situ reconstruction (rifampin-soaked graft or cryopreserved allograft). Endovascular stent-graft may stabilize hemodynamics as bridge therapy. Broad-spectrum antibiotics are initiated concurrent with surgery and continued long-term (6 weeks IV + lifelong oral).
AEF carries high mortality without treatment. Treatment is emergency surgery (graft removal + bowel repair + extra-anatomic bypass or in-situ graft) and prolonged antibiotic therapy. Delayed diagnosis increases mortality — emergent CTA should be performed when suspected.