Open and Endovascular Treatment of Anastomotic Aneurysms after Aortoaortic, Aortoiliac, and Aortofemoral Bypass

Misty D. Humphries, Gerald S. Treiman and Richard L. Treiman

Anastomotic aneurysms result from a disruption of the native artery–to–graft anastomosis. They are characterized by type (true or false), location (aortic, iliac, or femoral), and etiology (mycotic or nonmycotic). The majority are false aneurysms (pseudoaneurysms), with blood extravasation contained by periarterial tissue. True aneurysms can develop as the native artery itself dilates. Retroperitoneal anastomotic aneurysms often lead to life-threatening complications because of potential for rupture, and in the absence of major contraindications to intervention, they should be repaired. Several endovascular and open surgical options exist, but they are often complex and technically challenging.

Incidence

The overall incidence of aortic and iliac anastomotic aneurysm formation is likely underestimated by retrospective reviews because long-term graft surveillance is not the standard of care. These aneurysms are usually asymptomatic and, given their retroperitoneal location, are difficult to diagnose with physical examination. Studies using routine ultrasound surveillance to identify anastomotic abdominal aortic aneurysms estimate the incidence somewhere between 5% after 8 years and up to 27% after 15 years. Retrospective data on iliac anastomotic aneurysms estimate the incidence to be 6.3% at 15 years. Femoral anastomotic aneurysms after aortofemoral bypass are common, with an incidence in some reports as high as 24% at 15 years.

Pathophysiology

The development of a true or false anastomotic aneurysm is influenced by the indication for the initial arterial reconstruction. Patients treated for aneurysmal disease are more likely to develop true anastomotic aneurysms than patients treated for occlusive disease. In a study of 49 true anastomotic aneurysms, histologic evaluation of 28 resected arterial segments showed degeneration, with replacement of the media smooth muscle with acellular fibrous connective tissue, decrease or absence of elastic fibers, and hyaline degeneration of the adventitia.

Patients with the connective tissue disorders Ehlers–Danlos syndrome, α₁-antitrypsin deficiency, and Marfan’s syndrome or with systemic vasculitis such as Beçhet’s or Takayasu’s arteritis are predisposed to develop true anastomotic aneurysms owing to abnormalities of the native arterial wall.

Technical factors contributing to the development of anastomotic aneurysms include creation of the anastomosis in residual aneurysmal tissue, use of an oversized graft in relation to native arteries, end-to-side anastomosis, use of a Dacron graft, and endarterectomy of the arterial wall.

Several etiologies have been proposed for the development of anastomotic false aneurysms. Historically, the use of braided or silk suture was thought to be the main factor in their development. As an antigenic material, these sutures elicited an inflammatory response that destroys the suture over time. Widespread use of monofilament suture has made such an event no longer an issue. Other suggested causes of pseudoaneurysm formation include suture failure from overmanipulation or knotting, aggressive arterial wall endarterectomy, mismatch in the compliance of the vessel and graft, graft dilation, and, most importantly, infection.

Occult infection as a nidus of anastomotic aneurysms, especially of the femoral arteries, is commonly underestimated. After repair of 45 femoral pseudoaneurysms with no clinical sign of infection, 60% of the resected prosthetic graft specimens cultured were found to be positive for Staphylococcus species. Others have found graft infection rates as high as 80% after repair. The incidence of infection is unknown because microbiology laboratories often do not subject vascular graft material to ultrasonication to separate bacteria from the interstices of the material before culture. This likely led to erroneous reports of negative culture results. A postoperative wound infection with complete healing has been shown to increase the relative risk of femoral pseudoaneurysm formation by ninefold at 5 years.

Presentation

Anastomotic aneurysms have been diagnosed as early as a few months and as late as 23 years postoperatively. Allen found that 35% presented within 5 years. Factors associated with early development of anastomotic aneurysms are connective tissue disorders and graft infection. True aneurysms tend to occur late owing to the time needed for continued arterial wall degradation or graft material dilation. The mean time for development of all anastomotic aneurysms is approximately 8 years.

Although aortic and iliac anastomotic aneurysms are often asymptomatic, when symptoms develop, they are often insidious and include nonspecific abdominal pain, back pain, fatigue, and general malaise. Given their retroperitoneal location, aortic and iliac anastomotic aneurysms can grow to the point of palpation before symptoms develop. Nevertheless, in the largest series of aortic anastomotic aneurysms, 66% were identified in asymptomatic patients by computed tomography (CT) during workup for other conditions.

Increased size leads to risk of serious complications, including rupture or erosion into surrounding structures. Retrospective series have reported up to a 10% incidence of aortoenteric graft erosion following development of an aortic anastomotic aneurysm. Patients with aortoenteric fistula often come to the hospital with life-threatening gastrointestinal bleeding, and historically the mortality has approached 50%. Endovascular techniques have improved mortality by allowing intraaortic balloon occlusion to provide time for resuscitation and controlled open surgical repair.

Femoral anastomotic aneurysms typically manifest as a pulsatile groin mass that may be tender. A bruit or thrill may be present. As the aneurysm grows, patients can develop lower extremity edema or neuropathy from compression of the surrounding femoral vein and nerve. Rarely do these become large enough to rupture, but development of intraluminal thrombus in the aneurysm can lead to distal embolization, graft limb occlusion, or even acute limb-threatening ischemia. Typically, graft limb occlusion results in symptoms of claudication, with loss of the femoral pulse.

Evaluation and Diagnosis

Initial evaluation begins with a thorough history and systematic physical examination, including palpation of the abdomen and/or groin for a pulsatile mass, examination of distal pulses, and assessment for distal emboli. Diagnosis of an aneurysm at one anastomosis should prompt evaluation of other graft anastomoses given the 36% incidence of concurrent anastomotic aneurysms. Abdominal duplex scan may be useful in evaluating aortic and iliac anastomotic aneurysms, but its accuracy depends on the ability of the technologist, depth of the vessels, presence of gas in the gastrointestinal tract, and girth of the patient. Limitations of history and physical examination to make the diagnosis, combined with the severity of potential complications of intraabdominal anastomotic aneurysms, have prompted some authors to recommend yearly duplex surveillance even though its cost-effectiveness has not been established.

In patients in whom femoral anastomotic aneurysm is suspected, a duplex scan should be the initial diagnostic modality because it is easily obtained, avoids radiation, does not need contrast enhancement, and can accurately determine size and the presence of intraluminal thrombus.

Cross-sectional imaging of the aorta and iliac arteries with magnetic resonance angiography (MRA) or CT angiography (CTA) is the mainstay of surgical planning and should be obtained in all patients with confirmed or suspected aortic and iliac anastomotic aneurysms. MRA and CTA can diagnose the presence of the aneurysm, identify surrounding infection, delineate the relationship to surrounding structures, suggest a graft enteric fistula, and help plan operative reconstruction. Both provide detailed information about the relative proximity of the aneurysm to the surrounding arterial branches. Because MRA requires a dedicated radiologist to establish specific protocols and monitor image acquisition, the adequacy of MRA is particularly center-specific. CTA is much more widely available but requires administration of an ionizing contrast agent. The rapid acquisition of CTA also makes it more favorable in cases where hemorrhage or rupture is suspected.

Traditional angiography, although rarely needed, may be necessary for operative planning when CT images are obscured by arterial calcification or metallic hardware in the area of a planned intervention. Because angiography can only see the lumen of the vessel, identifying the exact location of the anastomosis may be limited in patients with true aneurysms and intraluminal thrombus. In cases where infection is suspected but not confirmed by cross-sectional imaging, technetium-labeled white blood cell scanning or combined positive emission tomography (PET)/CT may be able to identify an infected anastomotic aneurysm.

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