INTRODUCTION — Aortoenteric fistulae (AEFs), first described in the early 19th century by Sir Astley Cooper [1], are uncommon but life-threatening conditions. AEF is defined as an abnormal connection between the aorta and the gastrointestinal tract. It is most often the result of compression of an abdominal aortic aneurysm (AAA) against (primary cause), or erosion of an aortic prosthetic graft into (secondary cause), the surrounding gastrointestinal structures.
The clinical manifestations, diagnosis, and management of AEFs are reviewed here. The management of asymptomatic and general management of symptomatic AAAs are discussed separately. (See "Management of asymptomatic abdominal aortic aneurysm" and "Management of symptomatic (non-ruptured) and ruptured abdominal aortic aneurysm".)
DEFINITION AND CLASSIFICATION — Aortoenteric fistula (AEF) is a rare but potentially lethal disease. AEF is defined as an abnormal communication between the aorta (or aortoiliac tree) and the gastrointestinal system. It is most frequently due to primary aortic compression (eg, abdominal aortic aneurysm) against, or erosion of an aortic prosthetic graft into, the neighboring gastrointestinal organs. AEFs are most commonly a single communication between the aorta and a single organ, most often within the gastrointestinal tract. However, the aorta can fistulize to other organs concomitantly with the gastrointestinal tract, or to other organs independent of the gastrointestinal tract [2-4].
Two types of AEFs are recognized: primary aortoenteric fistula (PAEF) and secondary aortoenteric fistula (SAEF).
Primary aortoenteric fistula (PAEF) — Primary aortoenteric fistula (PAEF) arises de novo between the aorta and the gastrointestinal tract. Causes of PAEF include aneurysm (most common), foreign body, tumor, radiation therapy and infection (eg, tuberculosis, syphilis) [5-7]. One laboratory study of PAEFs in dogs demonstrated a role for both mechanical factors and aortic inflammation/infection in their development [8]. However, some feel that aortic inflammation/infection plays the more important role [9]. Septic aortitis with transient bacteremia, which may be due to a variety of pathogens [10-14], seeds bacteria onto the inner arterial surface and permits the formation of an aneurysm or false aneurysm that erodes into adjacent structures [15,16]. (See "Overview of infected (mycotic) arterial aneurysm", section on 'Etiology'.)
More than 75 percent of PAEFs involve the duodenum (aortoduodenal fistula), with most located in the third and fourth portions, where the duodenum is most closely related to the aorta [17]. However, PAEF may involve other portions of the gastrointestinal tract than the duodenum, such as the stomach (aortogastric fistula), jejunum (aortojejunal fistula), ileum (aortoilial fistula), or sigmoid colon (aortosigmoid fistula) [18-21].
Secondary aortoenteric fistula (SAEF) — Secondary aortoenteric fistula (SAEF) was first described in 1953 and can occur following virtually any aortic reconstruction [22], but most commonly SAEF involves a surgically placed aortic graft. SAEFs can also present after other aortic interventions, including endovascular aneurysm repair [23,24], and other endovascular procedures such as the use of bare metal aortic stents [25]. Interestingly, even in the presence of a thrombosed aortic prosthesis, SAEF can be postulated as the likely etiology and due to aortic graft pulsation; SAEF between a thrombosed aortic graft and the gastrointestinal tract has been reported [26]. Even in the absence of graft material or other vascular devices, SAEF can occur. As an example, SAEF has been reported after a remote infrarenal aorta ligation without any prosthetic graft within the abdomen [27].
The most frequent site of bowel connection in cases of SAEFs is the duodenum [17]. Involvement at other sites, such as the colon, is uncommon (4.8 to 6.6 percent of series reporting SAEFs) [17,28]. To exemplify the myriad of possible presentations, even rectal involvement, the furthest enteric element from the abdominal aorta, has been described, to our knowledge twice in the existing literature [29,30].
The exact pathogenesis of SAEFs is unknown. Two mechanisms of initiation have been proposed, but the sequence of events leading to maturation of the aortoenteric communication is not determined for every patient [31-33]. One mechanism relates to the constant pulsating motion of the graft against the bowel wall, and the other is adhesion of an already infected, inflamed graft to the bowel wall. Other mechanisms that are potentially involved include failure to properly place sutures through all layers of the aorta (with ensuing anastomotic bleeding and pseudoaneurysm formation), failure to adequately separate the graft and intestine (for instance, by using omentum between these structures), fragmentation of suture materials (particularly silk sutures) used to repair enterotomies, early reoperation for graft failure, and enterotomy at the index operation [34,35]. SAEF occurring after endovascular aneurysm repair is presumably related to dislodgment or migration of the device(s) from mechanical forces [36-40]. Continued pressurization of the aneurysm sac due to endoleak may also predispose to this fistula formation, particularly for large abdominal aortic aneurysms. Due to this possibility, among other reasons, surveillance and early intervention are necessary following all endovascular aneurysm repairs. (See "Endovascular repair of abdominal aortic aneurysm", section on 'Endograft surveillance'.)
Some investigators have differentiated between SAEFs that are true fistulous tracts from the graft's proximal suture line to the bowel lumen, and aortoenteric erosions, which are communications between the gastrointestinal tract and the external surface of the body of the prosthetic graft without actual fistulization [17]. The spectrum of gastrointestinal tract involvement leads to varying clinical manifestations. These include:
●Direct – Fistula formation with gastrointestinal bleeding. (See 'Massive hemorrhage' below and 'Acute bleeding' below.)
●Occult – Fistula formation without gastrointestinal bleeding. (See 'Suspected intestinal bleeding' below.)
●Indirect – Gastrointestinal bleeding without fistula formation. (See 'AEF with other presentations' below.)
EPIDEMIOLOGY AND RISK FACTORS — Aortoenteric fistula (AEF) is a rare entity that most vascular surgeons encounter fewer than a handful of times in their careers. Until the 1950s, all cases were primary aortoenteric fistulas (PAEFs). The increased availability of reconstructive vascular surgical procedures for aneurysm repair and reconstruction for severe aortoiliac atherosclerosis gave rise to secondary aortoenteric fistula (SAEF) as a complication of prosthetic reconstruction. The first SAEF was reported in 1953 in a 44-year-old woman three months after aortic repair [22]. Whether or not the incidence of AEF will increase or decrease in the future is uncertain. One might presume that the total number of AEFs will rise because of an increasing life expectancy and increasing population undergoing vascular repair. On the other hand, it is entirely possible that the incidence will decline owing to improved repair techniques and the development of more durable prosthetic materials, and the decrease in open aortic procedures.
SAEF is far more common than PAEF but is nevertheless rare [41]. The incidence of SAEF following aortic surgical reconstructions ranges from 0.36 to 1.6 percent; the incidence of PAEF has been reported to be less than 1 percent [42,43]. Because abdominal aortic aneurysms (AAAs) are frequently asymptomatic, it is not possible to determine the percentage of aneurysms that go on to fistulize primarily. Many patients die of AEF before it has been correctly diagnosed, and the incidence may be underestimated. As an example, only four patients were reported from the Dutch literature up to 1996. A study that sought to obtain more realistic figures on the incidence of this condition sent a questionnaire to all surgical clinics in the Netherlands and identified 35 additional cases [44].
AEF is more common in males compared with females, paralleling the incidence of AAA and aortic surgery. The male-to-female ratio is 3:1 for PAEF and 8:1 for SAEF [45]. Although AEFs are almost exclusively reported in the adult population, a case of PAEF was reported in a three-year-old child as a result of duodenal perforation after ingestion of a twig [46].
Risk factors — Abdominal aortic aneurysm (AAA) remains the most common risk factor of AEF, either as a cause of PAEF or following aortic repair leading to SAEF [15]. Aneurysm elsewhere in the aortoiliac tree can also be responsible, such as common iliac or internal iliac (hypogastric) artery aneurysm (either isolated or associated with AAA) [45,47]. Patients with a history of prior aortic surgery or intervention, with or without prosthetic graft reconstruction, are also at risk for AEF.
Other, less frequent causes of AEF include reflux esophagitis [48]; peptic ulcer disease [49]; erosion of distal duodenal diverticulum into the aorta [50]; pancreatic pseudocyst [51]; gastrointestinal malignancy [52]; erosion of embolization coils [53]; septic, nonaneurysmal aortitis [10]; remote complications of Billroth II gastric resection [54]; penetrating aortic ulcer [55]; enteral stenting [56]; foreign bodies [44,57,58]; and paraaortic radiation [59]. Rarely, syphilis, tuberculosis, aortic infection (bacterial, fungal), and collagen vascular disease can cause AEF [60-62]. For some patients, the precise etiology is not clear or never found [63-66].
SAEFs are thought to occur more often after aortic reconstructions for aneurysmal disease than for aortoiliac occlusive processes [9,31,67,68]. This belief seems to arise from an early report of 17 SAEFs, where only 18 percent of cases were seen after aortoiliac occlusive disease [31]. However, this finding has not been universally reported, and a number of SAEFs have been reported since after aortic reconstructions due to peripheral artery disease [42,69].
Correlations between the various approaches, type of aortic anastomotic reconstruction, type of graft material used, and the development of SAEFs have been speculated, though primarily through anecdotal experience. These suggest [70,71]:
●A higher occurrence of SAEFs after aortobifemoral bypasses compared with aortobiiliac or aortic tube grafts.
●Almost nonexistent occurrence using a retroperitoneal approach to aortic reconstruction.
●Fewer occurrences with an end-to-end compared with an end-to-side anastomosis for aortobifemoral bypasses.
●Although there appears to be an increased occurrence of SAEF with Dacron compared with expanded polytetrafluoroethylene (PTFE), for which few cases have ever been reported, it is impossible to correlate AEF with type of graft material, given the generalized preference for Dacron over PTFE in elective aortic vascular reconstructions.
CLINICAL MANIFESTATIONS — Aortoenteric fistula (AEF) is a devastating diagnosis regardless of its etiology. Bleeding is the most common initial presentation but does not always occur. The first description of primary aortoenteric fistula (PAEF) was put forth by Sir Astley Cooper in 1829 as "a man with a pulsating tumor seized with discharge of blood by stool and who died suddenly about 12 hours later [1]." At autopsy, "the jejunum had adhered to the aneurysmal bag and that sac had ulcerated into the intestine." Unfortunately, for many, this remains a common clinical presentation of AEF. (See 'Mortality' below.)
●AEF with gastrointestinal bleeding – Rupture of the aorta into a closely adherent portion of the gastrointestinal tract is the most common presentation of AEF. Bleeding episodes range from a minor hemorrhage (may be a herald bleed) to massive, life-threatening bleeding or overt rapid exsanguination, which is more common for secondary aortoenteric fistulas (SAEF). The type of SAEF (ie, anastomotic or paraprosthetic) influences the incidence of bleeding more than the location of the fistula. For SAEF, acute bleeding is more often seen in anastomotic AEFs due to direct communication of the aortic lumen with the gastrointestinal tract, whereas a chronic pattern of bleeding is seen more often with aortoenteric erosions [72]. In reviews of PAEF, hematemesis and melena were present in 32 to 78 percent of patients [73,74]. (See 'AEF with gastrointestinal bleeding' below.)
●AEF with other presentations – Other symptoms of AEF (particularly with SAEF) can include malaise, weight loss, overt sepsis, graft thrombosis with lower extremity ischemia, and other nonspecific symptoms [75]. Among patients with infected grafts in one review, 36 percent of the patients with SAEFs had no associated gastrointestinal bleeding [76]. Sepsis is one of the more common presentations among patients with aortoenteric graft erosion, and the treating physician needs to assume that the presence of aortoenteric graft erosion invariably represents an infected graft [17]. Aortoenteric graft erosion causing SAEF can occur in the absence of gastrointestinal bleeding. In these cases, bleeding does not occur because there is no true communication between the lumen of the prosthesis and the bowel. Almost one-third of AEFs involving the duodenum, and about two-thirds of AEFs involving small bowel or colon, do not bleed. (See 'Secondary aortoenteric fistula (SAEF)' above and 'AEF with other presentations' below.)
DIAGNOSIS — The diagnosis of aortoenteric fistula (AEF) is not easy because of its rarity. This is particularly the case for primary aortoenteric fistula (PAEF) where the presence of aneurysm is unknown, PAEF that has an etiology other than an aneurysm (eg, aortitis), or when it is idiopathic. For two-thirds of patients, a diagnosis of PAEF is made in the operating room [77]. Even with laparotomy, there can be some discrepancy regarding the accuracy of diagnosis. Laparotomy may be negative in one-half of cases [78]. Unfortunately, in spite of the multitude of diagnostic tools, as many as 50 percent of cases are diagnosed postmortem. A diagnosis of secondary aortoenteric fistula (SAEF) is typically made preoperatively more often than in PAEF cases but still requires an astute clinician to recognize this as a potential complication among patients who present with gastrointestinal bleeding after aortic interventions.
Because of the diagnostic difficulty, the diagnosis is often delayed. The reported time between developing symptoms until a correct diagnosis has been reached varies widely.
AEF with gastrointestinal bleeding — Early diagnosis of AEF associated with bleeding relies upon recognition of the typical "herald bleed," which is an episode of seemingly self-limited gastrointestinal bleeding that precedes a later catastrophic episode of hemorrhage. AEF must be kept in mind as a possible etiology of massive gastrointestinal bleeding in patients with prior aortic interventions, no matter how long since the intervention.
The classic triad of gastrointestinal bleeding, abdominal pain, and palpable mass occurs in only 6 to 12 percent of patients found to have AEFs [15,79]. When the etiology of AEF is an abdominal aortic aneurysm (AAA), a mass can be palpated in 25 to 70 percent [15,73,80]. The unreliability of clinical findings underscores the need to maintain a high index of suspicion in all cases of gastrointestinal bleeding, especially upper gastrointestinal tract bleeding. Further complicating the matter is the fact that patients with AAA/aortic intervention can have gastrointestinal bleeding due to other causes.
The very low incidence of this condition in the general population puts AEF low in the differential diagnosis of gastrointestinal bleeding. Thus, the condition is much less likely to be recognized by nonspecialty clinicians, who may not have sufficient awareness of this entity, and who may have the following misconceptions:
●That all AEFs will inevitably bleed
●That gastrointestinal bleeding in a patient with a previous prosthetic aortic reconstruction indicates unequivocally the presence of an AEF
●That an absence of bleeding excludes the presence of an AEF
●That AEF is excluded if another etiology for gastrointestinal bleeding is found
There is no absolute correlation between gastrointestinal bleeding and the presence or absence of an AEF. The demonstration of alternative upper gastrointestinal tract pathology by endoscopy also does not exclude the presence of a graft infection, with or without a fistula.
Massive hemorrhage — Hemodynamically unstable patients with massive bleeding and known AAA (unrepaired or repaired) should be taken directly to the operating room to make the diagnosis and perform repair (algorithm 1). For those in whom a diagnosis of AAA is unknown but is suspected by risk factors, urgent ultrasonography may identify the presence of the aneurysm but will not identify the AEF since overlying gas, which is commonly seen in the presence of an AEF or within the proximal bowel, may overshadow and obscure the anatomy. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Imaging symptomatic patients'.)
Patients with massive gastrointestinal hemorrhage (unknown or unproven AAA) require open surgical exploration to identify and control the source of bleeding. For those ultimately found to have PAEF, the diagnosis is made in the operating room in two-thirds of the patients [77]. For selected subsets of patients, arteriography with embolization therapy or stent placement may be able to temporize or treat massive gastrointestinal bleeding from an AEF. (See "Approach to acute upper gastrointestinal bleeding in adults", section on 'Treatment' and 'Open surgical repair' below and 'Arteriography' below.)
Acute bleeding — Hemodynamically stable patients with acute, but not massive, gastrointestinal bleeding generally undergo upper gastrointestinal endoscopy, regardless of etiology; however, the sensitivity of upper gastrointestinal endoscopy for diagnosing AEF is only about 50 percent [81-83]. Thus, for hemodynamically stable patients with a high suspicion for aortoenteric fistula (known AAA [unrepaired or repaired], prior aortic graft placement, aortic instrumentation), we suggest computed tomographic (CT) angiography as a first-line diagnostic study, which can usually be quickly obtained in most hospitals [84]. If the study is negative, upper endoscopy should be performed. Whereas upper endoscopy may be helpful for diagnosing a possible SAEF and ruling out other causes of gastrointestinal bleeding, the benefits of colonoscopy have been infrequently reported. A few reports have documented its use for evaluating AEF, particularly when there is apparent lower gastrointestinal bleeding in a patient with a history of an aortic intervention [85,86]. Hemodynamically unstable patients may become candidates for these studies after fluid resuscitation. (See "Approach to acute upper gastrointestinal bleeding in adults" and 'Massive hemorrhage' above.)
The sensitivity, specificity, and findings associated with AEF on CT angiography are discussed in the next section. (See 'Suspected intestinal bleeding' below.).
On upper endoscopy, careful inspection of the distal duodenum should be performed in the setting of unexplained brisk bleeding. More commonly, fresh blood or clots may be found in the third portion of the duodenum [87,88]. It is important to insert the endoscope to its limit, but thrombus and impacted graft material identified in the distal duodenum should not be dislodged. Endoscopy has the potential risk of inducing massive hemorrhage by dislodging fresh thrombus in the AEF, regardless if the AEF is primary or secondary [87]. No significant differences have been identified comparing medium with thin endoscopes [85,89].
Findings of gastritis or peptic ulcer disease, which are associated with AAA, may be misleading and may lead to a delayed diagnosis of PAEF or SAEF [90,91]. In one series of 7044 postmortem examinations, peptic ulcers were found three times more often in association with AAA than in the general population [92]. Thus, normal findings, or a positive finding of gastritis or ulcers without active bleeding, do not necessarily rule out an AEF.
Suspected intestinal bleeding — Owing to its widespread availability, CT angiography has become the first-line noninvasive imaging modality for evaluating suspected bleeding due to AEF, in spite of its variable sensitivity and specificity [93,94]. One study that compared CT findings with operative results reported a sensitivity of 94 percent and a specificity of 85 percent for detecting AEF [82]. (See "Evaluation of suspected small bowel bleeding (formerly obscure gastrointestinal bleeding)" and "Approach to acute lower gastrointestinal bleeding in adults".)
CT evaluation of the aorta should include unenhanced scanning with 5-mm collimation followed by arterial-phase CT performed with bolus tracking and 1-mm collimation. In addition, delayed imaging should be performed to detect endoluminal leakage when an aortic graft or stent is present. Oral contrast is not routinely used, because it may obscure subtle extravasation from the aorta into the bowel lumen. Multidetector CT (≥16 rows) is particularly useful when the rate of bleeding is slow and when detection of the proximal part of the fistula tract might be sufficient for the diagnosis [95].
The specific CT findings that correlate strongly with the presence of AEF include ectopic gas adjacent to or within the aorta (image 1), focal bowel wall thickening, discontinuity of the aortic wall, and extravasation of contrast material into the bowel lumen [82,83,96-98]. The fat plane that normally separates the aorta from the bowel is usually obliterated along the affected segment. An associated hematoma can sometimes be seen in the retroperitoneum or within the bowel wall or lumen. In addition, when gastrointestinal bleeding is the primary clinical manifestation, any CT features of perigraft infection should raise concern about the possibility of an SAEF. For patients with a prior aortic graft, the location of the fistula relative to the graft should be identified. In most cases, the site of the fistula is between the proximal suture line and the duodenum. However, one must remain alert to the possibility of communication directly through the graft material or a distal suture line. Focal bowel wall thickening adjacent to a vascular structure is a suggestive sign for AEF, but recognizing this can be challenging if the involved bowel loop is not distended with either gas or fluid. Intramural gas associated with aortic wall thickening in a bacteremic patient should raise suspicion for infectious aortitis. Other CT features include tethering or puckering of the bowel wall toward the aorta, and loss of the fat plane that normally separates the two. Extravasation of aortic contrast into the bowel lumen is extremely rare but is the most specific feature of AEF [97-99]. Leakage of enteric contrast material into the periaortic space is another rare but direct sign of AEF.
AEF with other presentations — Clinical suspicion is essential for a diagnosis of AEF in patients with no bleeding and nonspecific clinical findings in whom routine studies are often nondiagnostic. Such a presentation is more common for SAEF due to graft erosion, which often does not exhibit any bleeding.
Various diagnostic methodologies have been used to identify such SAEFs, including CT angiography [87], endoscopy [85], 18-fluorodeoxyglucose positron emission tomography [100], gallium 67 scanning [71,101], and arteriography [17,102]. These tests are often used as adjuvant techniques to detect PAEFs or SAEFs in those patients presenting with suspected bleeding, or in those without bleeding but with other nonspecific symptoms. Unfortunately, there is no single diagnostic investigation with a very high specificity and sensitivity. Therefore, it is not unusual for the results of these studies to be negative or equivocal and for the diagnosis to be made only at surgical exploration.
Nuclear medicine techniques are not conclusive evidence for a diagnosis of AEF but can add information that is helpful in difficult-to-diagnose cases of PAEF or SAEF. Scintigraphy performed with single photon emission computed tomography (SPECT) by using a radiotracer such as indium (111In) or technetium (99mTc) may complement CT by helping to detect a perigraft infection in an asymptomatic patient, with sensitivity ranging from 60 to 100 percent [77,100,103,104]. When the radiotracer is found in the bowel lumen on scintigrams, a relatively rare occurrence, its presence is highly suggestive of an AEF. Inflammatory bowel disease also may cause increased gastrointestinal uptake of these inflammation-targeting tracers, but the presence of such disease is usually known at the time of the scintigraphic evaluation. Tagged white cell scans have excellent sensitivity rates for the diagnosis of a graft infection, but have low specificity, with significant high false positive rates [75,105,106].
Esophagography with water-soluble contrast material may help confirm the presence of an esophageal perforation by documenting the extravasation of oral contrast material to an adjacent thoracic aortic graft. Rarely, the extraluminal oral contrast material may penetrate the aortic wall and suffuse the aortic graft [107].
ADDITIONAL EVALUATION
Arteriography — Arteriography is useful to define arterial anatomy, plan aortic reconstruction, and determine if endovascular repair is an option. The sensitivity, specificity, and findings associated with aortoenteric fistula (AEF) on computed tomography (CT) angiography are discussed in the section above. Magnetic resonance (MR) angiography may have similar sensitivity and specificity to CT angiography, but it is less useful because of its limited availability in the emergency setting, longer acquisition time, need for local technical expertise, and potential difficulties differentiating perigraft gas from aortic wall calcification. (See 'Suspected intestinal bleeding' above.)
Catheter-based arteriography is rarely used as the first-line imaging modality for the diagnosis of AEF. When extravasation of aortic contrast material into the adjacent intestinal lumen is seen, it is diagnostic of AEF; however, catheter-based arteriography rarely demonstrates the fistula, since bleeding is usually not active at the time of the examination [99]. In addition, it also has the potential risk of inducing recurrent or catastrophic bleeding in patients with AEF because of high-pressure injection of contrast [108]. Thus, if attempted, precautions need to be taken, such as being prepared for emergency laparotomy, if needed, by performing the procedure in an operating room setting. Therefore, CT arteriography is much more often utilized for those purposes.
Blood cultures — We routinely obtain blood cultures whenever a diagnosis of an AEF is suspected [96]. In addition, if a Clostridium septicum infection is documented, gastrointestinal or hematologic malignancies should be sought [109]. (See "Clostridial myonecrosis", section on 'Spontaneous gas gangrene'.)
Staging malignancy — Patients with unexplained weight loss or other risk factors for malignancy may have a tumor eroding into the aorta as the cause of AEF, which has been identified in imaging studies. Providing the patient's clinical status permits, staging the tumor may impact decision making with respect to proceeding with surgery, and choice of vascular reconstruction, if surgery is elected. (See 'Management' below.)
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of aortoenteric fistula (AEF) includes primarily other vascular etiologies. Nonvascular pathologies causing gastrointestinal bleeding in the presence of abdominal aortic aneurysm (AAA) or prior aortic intervention may confuse the picture. On imaging, potential mimics of AEF include retroperitoneal fibrosis, infected AAA, infectious aortitis, and, most important, perigraft infection without fistulization [77,97,104,105].
Other causes of gastrointestinal bleeding — There is no absolute correlation between gastrointestinal bleeding and the presence or absence of an AEF, and moreover, the demonstration of alternative upper gastrointestinal tract pathology by endoscopy as a cause of bleeding does not exclude its presence. (See 'Secondary aortoenteric fistula (SAEF)' above and 'Diagnosis' above.)
The incidence of upper gastrointestinal bleeding among patients with infected grafts, without an associated AEF, is 7 to 12 percent. One study of nine patients with prior aortic reconstruction and gastrointestinal bleeding identified inflammatory bowel disease, intestinal tubular adenomas, cecum angiodysplasia, dorsal pancreatic or right gastroepiploic artery aneurysms, gastroenterostomy stoma ulcers, left hemorrhoidal plexus bleeding, anorectal junction ulcers, and colon cancer as sources of bleeding [110]. There is also an association between peptic ulcers in patients with AAA and those with documented AEFs [92]. (See "Approach to acute upper gastrointestinal bleeding in adults" and "Approach to acute lower gastrointestinal bleeding in adults" and "Evaluation of occult gastrointestinal bleeding".)
Aortic infection without fistula — Because of their overlapping imaging features, AEF and perigraft infection may be difficult or impossible to differentiate. Although the computed tomography (CT) features of secondary aortoenteric fistula (SAEF) and perigraft infection are often similar, ectopic gas, loss of the fat plane, extravasation of aortic contrast material into the enteric lumen, and leakage of enteric contrast material into the paraprosthetic space are highly suggestive of AEF in a patient with gastrointestinal bleeding. (See 'AEF with gastrointestinal bleeding' above and "Overview of infected (mycotic) arterial aneurysm".)
MANAGEMENT — Treatment of aortoenteric fistula (AEF) includes initial resuscitation and hemodynamic support, antimicrobial therapy, and aortic repair (which requires graft removal in the case of secondary aortoenteric fistula [SAEF]). Without treatment, AEF is nearly uniformly fatal. The type and timing of repair is individualized, taking into account the clinical presentation (severity of bleeding or infectious process), type of AEF (primary or secondary), patient comorbidities, and aortic anatomy, among other factors. The initial care and resuscitation of the patient with gastrointestinal bleeding and hypovolemic shock are discussed separately (table 1). (See "Approach to acute upper gastrointestinal bleeding in adults" and "Treatment of severe hypovolemia or hypovolemic shock in adults".)
Antimicrobial therapy based on the sensitivity of the organisms recovered should be continued for a minimum of three months. Ideally, comanagement with an infectious disease service is recommended [111]. Longer-term antimicrobial therapy may be recommended when only a portion of a prosthetic graft has been removed (ie, portions that were not involved by the AEF). (See "Overview of infected (mycotic) arterial aneurysm", section on 'Antibiotic therapy'.)
Open repair of AEF is often complicated, requiring a patient with sufficient cardiac and respiratory reserve to tolerate the procedure. For patients who are not deemed fit for open repair, an endovascular approach has been suggested as a less invasive method to temporarily or definitively (often along with long-term antimicrobial therapy) manage the AEF [112]. Some have suggested using an aortic occlusion balloon at, or above, the level of the AEF for rapid control of the aortic bleeding [113]. (See "Endovascular methods for aortic control in trauma" and 'Endovascular repair' below.)
OPEN SURGICAL REPAIR
General approach — In general, treatment of aortoenteric fistula (AEF; primary or secondary) entails vascular control, debridement of infected and necrotic tissue (intestine and aorta), restoration of gastrointestinal continuity (if possible), and revascularization (local repair, in situ reconstruction, extra-anatomic reconstruction).
●Control the aorta – The aorta is controlled proximal to the fistula and distal to the extent that is needed. Vascular control above the renal arteries, or even above the mesenteric vessels, may be necessary. Some surgeons advocate gaining proximal control of the aorta above the diaphragm by thoracotomy for those with previous surgery [114]. Others have recommended a laparotomy with control of the aorta through the lesser sac, rather than by a thoracotomy, to minimize postthoracotomy complications [115-117]. An alternative method is a retroperitoneal approach to the aorta with the use of an aortic balloon catheter to gain proximal vascular control [118].
●Debride to healthy tissues – All infected and necrotic tissue must be debrided back to healthy tissue. The operative approach to all secondary aortoenteric fistulas (SAEFs) should assume that the prosthetic material is infected. This requires removal of the entire graft; attempts to repair the fistula and save the prosthetic implant are nearly certain to fail. After graft removal, the infrarenal aortic stump is oversewn with care to incorporate the prevertebral fascia for additional strength, and the stump should be reinforced (eg, omental flap) to decrease the risk of stump blowout. The distal aorta or iliac arteries may also need to be oversewn. Occasionally, a limited resection with suture repair of a minimally penetrating aortoenteric erosion is possible. Collected tissue should be sent for culture and sensitivity to guide antimicrobial therapy.
●Handle the intestinal defect – Following debridement, the affected intestine can be handled with either primary repair, ostomy, or with resection and primary anastomosis. (See "Bowel resection techniques" and "Overview of colon resection".)
●Revascularize – The nature and sequence of vascular reconstruction depends upon the type of AEF, which is discussed below. For primary aortoenteric fistula (PAEF), in situ aortic reconstruction using a prosthetic graft can generally be performed immediately, whereas for SAEF, the need for, type, and timing of revascularization is debated. (See 'Primary aortoduodenal fistula' below and 'Infected prosthetic graft' below.)
Primary aortoduodenal fistula — For PAEF, which is typically associated with abdominal aortic aneurysm (AAA), the fistula is repaired during the course of conventional, open aortic repair. Once the aorta is controlled above the fistula and distally, the duodenum is separated from the aorta to disclose the fistula and the aneurysm sac is opened. The duodenum can then be closed transversely in two layers, and aortic grafting is completed. The part of the aortic wall involved in the fistula should be excised, and omentum should be interposed between the graft and the duodenum. (See "Open surgical repair of abdominal aortic aneurysm".)
Infected prosthetic graft — The operative approach to all SAEFs should assume that the prosthetic material is infected. Once infected vascular tissue has been removed, the traditional approach is to oversew the infrarenal aorta and perform extra-anatomic reconstruction (eg, axillofemoral bypass grafting) to restore blood flow to the lower extremities. Alternatively, in the absence of gross purulence or contamination at the site of the fistula, in situ reconstruction can be performed [111,119]. In situ graft options include rifampin-bonded or silver-coated Dacron grafts [120-124], cryopreserved arterial or venous allografts [125-129], and vein graft reconstruction [130,131]. The timing of revascularization is controversial. The need for in situ reconstruction has increased due to a reduced length of infrarenal aortic tissue available to allow the aorta to be oversewn at the time of graft removal when infection occurs in the setting of endovascular abdominal aortic repair.
The optimal timing of revascularization for SAEF is debated [17,132,133]. Some surgeons believe that viability of the extremities can be predicted through clinical assessment after aortic interruption before proceeding to extra-anatomic bypass (axillofemoral and femorofemoral). However, colonic ischemia and/or extremity ischemia can occur even when the limbs appeared viable during operation, making it prudent to proceed with immediate bypass except perhaps in those with the greatest surgical risks. After removal of an end-to-end aortic graft, immediate reconstruction will more than likely be necessary. However, if the resected graft had been placed end-to-side, reestablishment of circulation through the native aorta may obviate this additional procedure. Likewise, if there has been a previous major leg amputation, extra-anatomic bypass may not be needed. An alternative strategy is to reverse the order of the procedure, in which revascularization by axillobifemoral bypass is performed first, unless laparotomy is required initially to confirm the diagnosis, followed by delayed graft removal [132]. This option may be preferred in hemodynamically stable patients; bleeding must be addressed first in hemodynamically unstable patients.
Complications — The major complications after an open repair include AEF recurrence, aortic stump disruption (blowout), and infection of the newly placed graft. Aortic stump blowout is the most common complication, usually caused by residual infection.
ENDOVASCULAR REPAIR — Given the high morbidity and mortality associated with traditional open repair of aortoenteric fistula (AEF), there is considerable interest in adapting endovascular aneurysm repair techniques (EVAR). Endovascular options that can be used to manage patients with AEF include endovascular balloon occlusion of the aorta, endovascular embolization, and stent-graft repair.
Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) has been proposed as a means to control bleeding from the aorta to provide a window for resuscitation, or a bridge to definitive care, similar to its use in managing ruptured abdominal aortic aneurysms (AAAs), or abdominal/pelvic hemorrhage as a result of trauma. The technical details for accomplishing REBOA are reviewed separately. (See "Endovascular methods for aortic control in trauma".)
Most initial reports in the early 2000s using stent-grafts represented anecdotal experiences [70,134-137]. Later systematic reviews seem to confirm that using endovascular techniques as a bridge in unstable patients, followed by definitive open repair in appropriately selected candidates, can improve early outcomes compared with immediate open surgery; however, the long term is associated with higher rates of recurrent infection and bleeding [138-140]. In one of these reviews, 59 patients with AEF were managed with endovascular stent-grafts [138]. Perioperative mortality was 8.5 percent, and 12- and 24-month mortality rates were 15 and 19 percent, respectively. Recurrent bleeding occurred in 19 percent, and sepsis occurred in 32 percent, which was seen more often in patients who did not have intestinal repair. In a larger review that identified 823 patients with secondary aortoenteric fistulas (SAEFs), in-hospital mortality was overall 31 percent and was significantly higher among those undergoing open surgery compared with EVAR (34 versus 7 percent) [139]. The incidence of late sepsis was higher for EVAR compared with open surgery (42 versus 19 percent at two years). The early survival benefit of EVAR was blunted during long term follow-up but remained significant, suggesting that a staged approach with early conversion open repair (in situ vein aortic replacement) may be the best approach for patients who can withstand subsequent surgery.
Other adjunctive endovascular techniques have been used, including coil embolization [141], the use of an endovascular plug (eg, Amplatzer) [142], endoscopic injection of fibrin sealant for the fistula [143], or N-butyl 2-cyanoacrylate injection into the fistula tract [144]. These are also predominantly used as a temporizing measure to control hemorrhage and provide a window of opportunity to plan definitive treatment, but in some cases are meant as an adjunct to palliative treatment in poor risk surgical patients.
Potential indications for an endovascular approach for the management of AEF associated with AAA are similar to aneurysms that have not fistulized, including patients in whom open surgical repair is not feasible (eg, hostile abdomen), and patients who have a prohibitive surgical risk with open repair. A staged combination of EVAR for acute bleeding combined with aggressive infection control (systemic antibiotics, minimally invasive abscess drainage, and fistula tract closure) might be the better option for fragile patients. For patients who are fit for open repair, EVAR can be used as a bridging procedure to definitive repair, particularly in the setting of systemic infection [145]. Most surgeons advocate the use of endovascular stent grafting as a temporizing measure, rather than definitive treatment, since rebleeding or reinfection can still occur, most often in the mid-term or long-run follow-up [69,113,140,146-148].
The use of stent-grafts in patients with SAEFs relies on the presence of a cuff of normal aorta between the renal arteries and the graft suture line, which is present in most cases. However, it may be difficult to identify the suture line on the computed tomography (CT) scan. The original prosthetic graft dilates within months of implantation, and the distinction between the neck and graft can be quite difficult. As such, a large stent-graft (>30 mm in diameter) is usually required. The presence of a short graft body length in a bifurcated graft may pose a problem. Most commercial stent-grafts have a body length of ≥70 mm in length (table 2), which is longer than the 30- to 50-mm length typically used for an end-to-side bifurcated aortic graft. The proximal extension cuffs that are available with commercial grafts may be useful in such a situation. Given that most stent-grafts will be used as a temporizing measure and will be removed during open surgical repair at a later date, the use of devices with suprarenal fixation can be problematic, as subsequent removal becomes very difficult. If a device with suprarenal fixation is used, the aorta will need to be clamped above the renal arteries, or even above the mesenteric vessels, or a balloon catheter can be used to gain vascular control. The covered section of the graft can be excised by dividing the sutures that articulate it to the bare suprarenal stent, and the bare stent (the metallic part, without any prosthetic material) can be left behind as it is firmly attached to the aorta with its barbs.
Rebleeding/reinfection — Among patients with primary aortoenteric fistula (PAEF), clinical or radiographic evidence of stent-graft reinfection is low [112,145,147,149-152]. However, for SAEF in the presence of systemic infection, patients treated using an endovascular approach alone will require several hospital readmissions for septic episodes in the form of spiking fever, rigors, and general malaise, but fortunately bleeding is uncommon. CT scans have demonstrated endografts directly exposed to bowel contents as a cause for recurrent fevers [134]. One report noted an almost threefold increased risk of persistence/recurrence of infection for SAEF treated with a stent-graft compared with PAEF [140].
PREVENTION — Preventing direct contact between the synthetic graft and bowel by closure of native tissues over the graft can help avoid the development of an aortoenteric fistula (AEF) after aortoiliac reconstructive surgery. Other techniques include the use of viable pedicles of the greater omentum [119], or other tissue [153], or prolonged antimicrobial therapy. (See "Open surgical repair of abdominal aortic aneurysm", section on 'Abdominal closure'.)
For abdominal aortic aneurysm repair, coverage of the graft can usually be accomplished by reapproximating the cut edges of the aneurysm sac. In the case of an aortofemoral bypass, the posterior peritoneum near the inferior mesenteric vein on the left can be approximated to pre- and paracaval retroperitoneal tissue on the right. This is usually easily accomplished during end-to-end reconstruction but may be difficult in some cases of end-to-side reconstruction because of insufficient tissue. When difficulty is encountered, covering the graft with an omental flap is an effective method of preventing erosion. If the omentum has been surgically removed, or is unusable for some other reason, an alternative graft can be used, or a prosthetic patch can be used to prevent direct contact between the vascular graft and the duodenum. Because of its softness, elasticity, and thickness, we prefer to use expanded polytetrafluoroethylene for this purpose [34]. Some have advocated avoiding deliberately replacing the duodenum back into a position that overlies the aortic prosthesis.
MORTALITY — Early diagnosis and aggressive surgical treatment are the best ways to achieve optimal results in these patients. Outcomes depend upon the speed of diagnosis, the patient's medical status, the severity of infection, and the anatomic site of the aorta involved. Many patients with aortoenteric fistula (AEF) die before an accurate diagnosis is made due to its variable clinical manifestations and insufficient awareness of this rare entity among nonspecialty clinicians.
Without surgery, AEF is nearly uniformly fatal [90,154]. However, in spite of technological advances in surgical and endovascular techniques and perioperative care, AEF is still associated with high rates of morbidity and mortality. Surgical treatment of secondary AEFs has been associated with mortality ranging from 14 to 70 percent [155-158]. A review of 118 cases of AEF found an overall and surgical mortality of 86 and 36 percent, respectively; most of the patients who died did so before diagnosis or surgical intervention [80].
SUMMARY AND RECOMMENDATIONS
●Aortoenteric fistula (AEF) is an uncommon but life-threatening condition. AEF is defined as an abnormal connection between the aorta (or aortoiliac tree) and the gastrointestinal tract. The most frequent site of the bowel connection is the duodenum. (See 'Introduction' above and 'Definition and classification' above.)
●Two types of AEFs are recognized: primary aortoenteric fistula (PAEF) and secondary aortoenteric fistula (SAEF).
•PAEF arises de novo between the aorta and the bowel, most often the result of compression of an abdominal aortic aneurysm (AAA) against the bowel. Mechanical factors and aortic inflammation/infection may have a role in their development. (See 'Primary aortoenteric fistula (PAEF)' above.)
•SAEF can develop following virtually any type of surgical aortic reconstruction but is most commonly due to erosion of a surgically placed aortic prosthetic graft into the surrounding bowel. SAEFs can also occur after other aortic interventions, including endovascular aneurysm repair. Rarely, SAEF has been reported to occur in the absence of a prosthetic graft. (See 'Secondary aortoenteric fistula (SAEF)' above.)
●SAEF is far more common than PAEF but is nevertheless rare. AAA remains the most common risk factor of AEF, either as a cause of PAEF or following repair leading to SAEF. AEF is more common in males compared with females, paralleling the incidence of AAA and aortic surgery. (See 'Epidemiology and risk factors' above.)
●Gastrointestinal bleeding is the most common presentation of AEF due to rupture of the aorta into a closely adherent portion of bowel. The severity of bleeding ranges from a minor hemorrhage, which may represent a herald bleed, to massive, life-threatening bleeding or overt rapid exsanguination, a presentation that is more common with SAEFs. Other symptoms of AEF can include malaise, weight loss, overt sepsis, graft thrombosis with lower extremity ischemia, or other nonspecific symptoms. (See 'Clinical manifestations' above.)
●The classically described clinical triad of bleeding, abdominal pain, and a palpable abdominal mass is not at all reliable. Thus, the diagnosis of AEF relies on a high index of suspicion. AEF must be kept in mind as a possible etiology of gastrointestinal bleeding in any patient with known AAA or prior aortic intervention, no matter how long ago. The diagnosis may not be easy to make and is often delayed, particularly when the presence of AAA is unknown, the AEF has an etiology other than an aneurysm (eg, aortitis), or when it is idiopathic. (See 'Diagnosis' above and 'Risk factors' above.)
•Hemodynamically unstable patients with massive bleeding and known AAA (unrepaired or repaired) should be taken directly to the operating room for control of bleeding and repair (algorithm 1). For those in whom a diagnosis of AAA is unknown, but suspected by risk factors, urgent ultrasonography may identify the presence of the aneurysm but will not identify the AEF. (See 'Massive hemorrhage' above and "Management of symptomatic (non-ruptured) and ruptured abdominal aortic aneurysm".)
•Hemodynamically stable patients with acute gastrointestinal bleeding generally undergo upper gastrointestinal endoscopy; however, the sensitivity of upper gastrointestinal endoscopy for diagnosing AEF is only about 50 percent. Thus, for patients with a high suspicion for AEF, we suggest CT angiography as a first-line study, which can be quickly obtained in most hospitals. If the study is negative, upper endoscopy should be performed with careful inspection of the distal duodenum. Thrombus and impacted graft material identified in the distal duodenum should not be dislodged. (See 'Acute bleeding' above and "Approach to acute upper gastrointestinal bleeding in adults" and "Approach to acute lower gastrointestinal bleeding in adults".)
•For patients with suspected intestinal bleeding and possible AEF, we suggest CT as a first-line noninvasive imaging modality. However, because of overlapping CT features, AEF and perigraft infection may be difficult or impossible to differentiate, and adjunctive studies may be needed to aid in diagnosis.
●The specific CT findings that correlate strongly with the presence of AEF include ectopic gas adjacent to or within the aorta, focal bowel wall thickening, discontinuity of the aortic wall, and extravasation of contrast material into the bowel lumen. Any CT features of perigraft infection should raise concern about the possibility of an SAEF. (See 'Suspected intestinal bleeding' above and 'AEF with other presentations' above and "Overview of infected (mycotic) arterial aneurysm".)
●Treatment of AEF includes initial resuscitation and hemodynamic support, antimicrobial therapy, and aortic repair (which requires graft removal in the case of SAEF). Without treatment, AEF is nearly uniformly fatal. The type and timing of repair is individualized, taking into account the clinical presentation (severity of bleeding or infectious process), type of AEF (primary or secondary), patient comorbidities, and aortic anatomy, among other factors. (See 'Management' above.)
●Options for repair include open surgical (staged, nonstaged) and endovascular repair. For patients who are not deemed fit for open repair, which can be a lengthy and complicated procedure, an endovascular approach has been suggested as a less invasive method to temporarily or definitively manage the AEF.
•Open surgical management of AEF involves vascular control, debridement of infected and necrotic tissue (intestine and aorta), restoration of gastrointestinal continuity, and revascularization (local repair, in situ reconstruction, extra-anatomic reconstruction). (See 'Open surgical repair' above.)
•Endovascular options, either alone or in conjunction with a staged, open repair include endovascular balloon occlusion of the aorta, endovascular embolization (coil, fibrin glue, endovascular plug), and stent-graft repair. These techniques are predominantly used as a temporizing measure to control hemorrhage and provide a window of time to resuscitate the patient and plan definitive treatment. In the presence of systemic infection, endovascular repair alone is often followed by repeat infection. In some cases, endovascular methods can be used for palliative treatment of patients with poor surgical risk. (See 'Endovascular repair' above.)
●The treatment of AEF remains associated with significant morbidity and mortality. Outcomes depend upon the speed of diagnosis, the patient's medical status, the degree of infection, and the anatomic site of the aorta involved. Early diagnosis and aggressive surgical treatment are the best ways to achieve optimal outcomes in these oftentimes very ill patients. (See 'Mortality' above.)
