Risk of Aortoenteric Fistula After Aortobifemoral Bypass
Aortoenteric fistula occurs in up to 4% of patients after aortobifemoral bypass surgery, representing a rare but potentially life-threatening complication with high mortality rates. 1
Definition and Epidemiology
Aortoenteric fistulas (AEFs) following aortobifemoral bypass are classified as secondary AEFs, which result from erosion of an aortic vascular graft into the bowel lumen. Key epidemiological facts include:
- Incidence rate: Up to 4% of patients after abdominal aortic aneurysm repair 1
- Most common site: Third portion of the duodenum 1
- Timing: Can develop anywhere from 1-7 years after the initial procedure 2
- Mortality: Extremely high (30-40%) even with appropriate surgical intervention 1, 3
Pathophysiology and Risk Factors
The development of aortoenteric fistulas after aortobifemoral bypass typically occurs through several mechanisms:
- Direct erosion of the graft into adjacent bowel, typically at the suture line
- Infection of the graft material leading to perigraft inflammation
- Pseudoaneurysm formation causing pressure on adjacent bowel structures 4
- Mechanical factors including graft migration or severe angulation causing repetitive friction wear and mucosal tear 1
Clinical Presentation
The classic presentation includes:
- Gastrointestinal bleeding (89% of cases) - may be intermittent "herald bleeds" or massive exsanguination 2
- Melena (most common)
- Hematemesis
- Hematochezia (less common)
- Sepsis - fever, elevated white blood cell count, increased sedimentation rate 2
- Abdominal or back pain
- Pulsatile abdominal mass (rare)
Diagnostic Approach
Diagnosis requires a high index of suspicion in any patient with history of aortobifemoral bypass who presents with GI bleeding. The most useful diagnostic tools include:
- CT angiography - sensitivity >90% when combined with clinical suspicion 3
- Look for: Perigraft fluid, air bubbles, loss of fat plane between aorta and bowel
- Upper GI endoscopy - may visualize the graft material or fistula 3
- Combination approach - CT plus endoscopy offers the best chance of detection 4
Management
Management of aortoenteric fistula is surgical and should be considered a medical emergency:
Initial stabilization
- Fluid resuscitation
- Blood product transfusion
- Broad-spectrum antibiotics
Definitive surgical management - options include:
- Open surgical repair with graft excision - the gold standard approach 1
- Extra-anatomic bypass (axillobifemoral bypass) followed by graft removal - preferred for cases with gross purulence 1
- In situ reconstruction with a new graft - may be considered in selected cases 1
- Endovascular therapy (EVT) - may be used as a bridge to definitive open repair to control acute bleeding 1
Antimicrobial therapy
- Initial parenteral antibiotics for 6 weeks to 6 months
- Consideration of lifelong suppressive antibiotic therapy, especially with retained endovascular devices 1
Prognosis and Outcomes
- Early postoperative mortality remains high at approximately 30% 3
- Recurrence rates of fistulae: 22-49% depending on surgical approach 1
- Sepsis rates: 30-72% depending on surgical approach 1
- Reoperation rates: 36-70% depending on surgical approach 1
Prevention and Surveillance
While specific guidelines for surveillance after aortobifemoral bypass are limited, the American College of Cardiology/American Heart Association recommends:
- Regular imaging surveillance after aortic repair 1
- Para-anastomotic aneurysms after open AAA repair tend to occur late, with estimated incidence rates of 1%, 6%, and 27% to 35% at 5,10, and 15 years postoperatively, respectively 1
- Consider surveillance imaging every 5 years after open AAA repair 1
Conclusion
Aortoenteric fistula represents a serious complication after aortobifemoral bypass with high mortality rates. Early recognition through appropriate imaging and prompt surgical intervention are essential to improve survival outcomes.