Overview
Definition:
An aortoenteric fistula (AEF) is an abnormal communication between the aorta or a prosthetic aortic graft and the gastrointestinal tract
It is a rare but life-threatening complication, most commonly occurring as a secondary event after aortic reconstructive surgery, particularly with prosthetic grafts
Primary AEF without prior surgery is exceptionally rare.
Epidemiology:
Secondary AEF occurs in 0.4-2% of patients with prosthetic aortic grafts
The incidence of primary AEF is exceedingly low
Risk factors for secondary AEF include prosthetic graft infection, previous abdominal surgery, radiation therapy to the abdomen, and immunocompromise
The most common location for a secondary AEF is between the duodenum and an infrarenal aortic graft.
Clinical Significance:
AEF represents a surgical emergency due to the high risk of massive hemorrhage and sepsis
Prompt diagnosis and aggressive management are crucial for patient survival
Mortality rates remain high, often exceeding 50%, emphasizing the need for rapid intervention and multidisciplinary care.
Clinical Presentation
Symptoms:
Abdominal pain, often severe and colicky
Gastrointestinal bleeding, ranging from melena to massive hematemesis or hematochezia
Intermittent herald bleeding episodes followed by frank exsanguination
Fever and systemic signs of infection if graft sepsis is present
Signs of hemodynamic instability: hypotension, tachycardia, pallor, diaphoresis.
Signs:
Abdominal tenderness, guarding, or rigidity
Palpable abdominal pulsatile mass (if aneurysm is present)
Signs of hypovolemic shock
Evidence of ongoing gastrointestinal bleeding
Signs of sepsis: fever, tachycardia, hypotension.
Diagnostic Criteria:
No specific diagnostic criteria exist
diagnosis is based on high clinical suspicion in the context of risk factors and confirmed by imaging and/or endoscopy
The classic triad of abdominal pain, gastrointestinal bleeding, and a pulsatile abdominal mass is often absent or may not present simultaneously.
Diagnostic Approach
History Taking:
Detailed history of prior aortic surgery, particularly the type and timing of graft placement
History of abdominal radiation or infection
Onset, severity, and character of abdominal pain
Pattern and volume of gastrointestinal bleeding
Presence of systemic symptoms like fever
Red flags: any patient with a history of aortic graft presenting with unexplained gastrointestinal bleeding or abdominal pain requires a high index of suspicion.
Physical Examination:
Thorough abdominal examination to assess for tenderness, masses, and pulsatility
Complete cardiovascular assessment for signs of shock
Systemic examination for signs of infection.
Investigations:
Laboratory tests: Complete blood count (CBC) for anemia and leukocytosis
Coagulation profile (PT, PTT, INR)
Blood type and crossmatch for urgent transfusion
Renal function tests
Imaging modalities: Computed Tomography Angiography (CTA) is the investigation of choice, visualizing the aorta, graft, and potential fistulous tract, and identifying extraluminal air or fluid suggestive of infection
Upper or lower endoscopy may be diagnostic if bleeding is active and imaging is inconclusive, but carries a risk of precipitating massive hemorrhage and should be performed with extreme caution and in conjunction with surgical readiness
Ultrasound may detect perigraft fluid collections but is less sensitive for the fistula itself.
Differential Diagnosis:
Peptic ulcer disease with bleeding
Esophageal varices with bleeding
Malignancy of the gastrointestinal tract
Mesenteric ischemia
Other causes of massive GI bleeding
Ruptured abdominal aortic aneurysm (AAA) without fistula.
Management
Initial Management:
Immediate resuscitation with aggressive fluid and blood product replacement to stabilize hemodynamics
Secure at least two large-bore intravenous access lines
Prompt consultation with vascular surgery and gastrointestinal services
Preparation for urgent surgical intervention
Nasogastric tube insertion to decompress the stomach and monitor for bleeding
Broad-spectrum antibiotics for suspected graft infection.
Medical Management:
Primarily supportive and aimed at hemodynamic stabilization
Transfusion of packed red blood cells to maintain hemoglobin levels >7-8 g/dL
Fresh frozen plasma and platelet transfusions as guided by coagulation status and active bleeding
Vasopressors may be required in severe shock
Antiemetics to control nausea and vomiting
Proton pump inhibitors to reduce gastric acidity.
Surgical Management:
The definitive management is surgical repair
Options include: 1
Excision of the infected graft with extra-anatomic bypass (e.g., axillofemoral bypass) and wide debridement of infected tissue
2
In situ graft repair (less common, higher risk of recurrence)
3
Ligation of the aorta if bypass is not feasible
The choice of procedure depends on the patient's hemodynamic status, the extent of infection, and the surgeon's expertise
If the fistula involves the duodenum, repair of the enteric defect is also necessary, often with diversion (e.g., duodenal diversion, gastrostomy).
Supportive Care:
Continuous hemodynamic monitoring in an intensive care unit
Close monitoring of urine output
Nutritional support, often parenteral initially
Strict glycemic control
Prophylaxis for deep vein thrombosis
Postoperative physiotherapy.
Complications
Early Complications:
Massive hemorrhage leading to exsanguination and death
Sepsis and septic shock
Acute kidney injury
Respiratory distress
Myocardial infarction
Stroke
Graft dehiscence.
Late Complications:
Graft limb occlusion or stenosis
Pseudoaneurysm formation
Recurrent graft infection
Chronic abdominal pain
Enterocutaneous fistula
Incisional hernia.
Prevention Strategies:
Judicious use of prosthetic grafts, considering biologic grafts in high-risk patients
Meticulous surgical technique during aortic reconstruction to minimize contamination
Early diagnosis and management of graft infection
Careful antibiotic selection and duration for infected grafts.
Prognosis
Factors Affecting Prognosis:
The most significant factor is the speed of diagnosis and intervention
Hemodynamic stability at presentation
Presence and severity of sepsis
The extent of aortic and enteric involvement
Patient comorbidities
The type of surgical repair performed.
Outcomes:
Mortality rates remain high, historically ranging from 40-90%, although aggressive modern management has led to some improvement
Survival is significantly improved with prompt surgical treatment before exsanguination
Long-term survival depends on successful graft limb salvage and absence of recurrent infection.
Follow Up:
Long-term follow-up is essential, typically with vascular surgery and gastroenterology
Regular clinical assessment for signs of recurrent infection or graft complications
Imaging studies (CTA, ultrasound) may be used to monitor the integrity of any repaired or replaced graft
Monitoring for gastrointestinal symptoms and nutritional status.
Key Points
Exam Focus:
AEF is a surgical emergency
prioritize immediate resuscitation and urgent surgical consultation
CTA is the investigation of choice
The management involves controlling the hemorrhage, treating infection, and reconstructing the aorta, often with extra-anatomic bypass
Primary vs
secondary AEF distinction is important
Recognize the "herald bleed" phenomenon.
Clinical Pearls:
Always consider AEF in patients with a history of aortic grafts presenting with unexplained GI bleeding or abdominal pain
Maintain high index of suspicion and involve vascular surgery early
Aggressive resuscitation is paramount before any diagnostic intervention that could precipitate massive bleeding
Surgical mortality is high, but preventable if treated promptly
Consider biologic grafts in certain high-risk scenarios to reduce infection rates.
Common Mistakes:
Delaying surgical consultation due to uncertainty or attempts at conservative management
Performing endoscopy or colonoscopy without adequate surgical preparedness, risking catastrophic hemorrhage
Underestimating the severity of bleeding and failing to transfuse adequately
Inadequate debridement of infected tissue
Not addressing the enteric defect appropriately.