Type II endoleak accompanied by an arteriovenous fistula between the inferior mesenteric artery and the inferior vena cava as a complication of endovascular aneurysm repair

Abstract

Endovascular aneurysm repair (EVAR) has become one of the most important treatments for aortic abdominal aneurysm. This method has some possible complications, including a type II endoleak (T2E). When coexisting with arteriovenous fistulas (AVF), T2E can lead to serious hemodynamic consequences and organ failure. This report describes the management of a patient with T2E coexisting with AVF following an EVAR and re-EVAR procedure. Although T2E itself may be treated with a conservative approach in some cases, in the presented patient an operative approach was necessary because of coexisting AVF. In addition, due to unusual hemodynamic conditions created by concomitant ACF and T2E, fistula closure was obtained as a result of transarterial inferior mesenteric artery embolization. Post-EVAR imaging, including ultrasound and computed tomography angiography, has proven to be essential when caring for these patients.

Endovascular aneurysm repair (EVAR) is a standard treatment modality for aortic abdominal aneurysms (AAA).¹ Endoleaks are the most common complication following EVAR, and type II endoleak (T2E) typically occurs in 10% to 30% of patients.^1,2 Although T2E are usually self- limiting, they may co-exist with an arteriovenous fistula (AVF), most of which are aortocaval fistulas (ACF), leading to hemodynamic sequelae including organ malperfusion and persistence of both the AVF and the T2E.^3,4 Herein we describe a patient who developed a T2E with a concomitant AVF involving the inferior mesenteric artery (IMA) and inferior vena cava (IVC) following EVAR. This was successfully managed with transarterial embolization of the IMA.

CASE REPORT

An 84-year-old man presented to the emergency department with a 3-week history of left flank and suprapubic pain. His past medical history included a standard elective EVAR for an infrarenal AAA 8 years before, hypertension, diabetes, ischemic heart disease, and peptic ulcer disease. His last EVAR follow-up was a Duplex ultrasound (DUS) 6 years earlier which did not show sac expansion. On admission, the patient had acute kidney injury with an estimated glomerular filtration rate (eGFR) of 24 mL/min/1.73 m² and creatinine of 2.73 mg/dL. An echocardiogram revealed impaired diastolic function with preserved ejection fraction. Computed tomography angiography (CTA) showed a type IIIa endoleak resulting from a separation of the main body and one of the limbs, in addition to a migration of the proximal part of the stent, prompting a decision to carry out an endograft relining. The procedure was performed under general anesthesia via bilateral percutaneous access of the common femoral arteries. An Endurant IIs^TM (Medtronic, Dublin, Ireland) device was used with a limb extension. The completion angiogram was normal and the patient was discharged home 3 days later with an eGFR of 45 mL/min/1.73 m².

A follow-up CTA a month later revealed a T2E with a fistula between the IVC and IMA (Figure 1a) in addition to the presence of Riolan’s arch (Figure 1b). A repair of the T2E was performed a week later. Following percutaneous femoral access and retrograde catheterization of the superior mesenteric artery, the IMA was accessed via the Riolan’s arch and embolized using 3 x Tornado^TM Embolization Coils (Cook Medical, Bloomington, IN) (Figure 1c). Completion angiogram showed a marginal contrast leak into the IVC. A decision was made to complete the procedure at this point. The patient was discharged on the third day after the procedure with a significant improvement in renal function (eGFR 139 mL/min/1.73 m² and creatinine 0.59 mg/dL). The follow-up CTA at 3 weeks confirmed closure of the fistula and absence of sac expansion or endoleak (Figure 1d). DUS performed at 6 months confirmed these findings.

Figure 1.

(a) Axial view of computed tomography angiography showing fistula between the inferior vena cava and inferior mesenteric artery. The arrow points to contrast enhancement within the compressed inferior vena cava. (b) 3D reconstruction of computed tomography angiography demonstrating Riolan’s arch (arrows). (c) Digital subtraction angiography demonstrating successful embolization of the inferior mesenteric artery with stainless steel coils. (d) Computed tomography angiogram performed 3 weeks after the stent graft relining, with axial imaging demonstrating contrast in the limbs of the graft and no contrast in the aneurysm sac.

DISCUSSION

This is the first reported case of an AVF between the IVC and the IMA feeding a T2E. AVFs involving IMA remain rare; all 40 reported cases describe AVF originating from the portal system.⁵ On the contrary, our case describes the AVF between the IMA and IVC, resulting in aortocaval communication. While ACFs typically arise due to inflammation and pressure leading to necrosis of the vessel wall,⁶ the pathophysiology of the fistula described in this case remains intriguing. The AVF did not involve the aneurysm sac directly, and the endograft relining procedure was performed without known complications. We speculate that the IVC compressed by the aneurysm sac was pressed against the adjacent IMA (Figure 1a), leading to erosion of the wall and formation of a fistula.

ACF is rare, accompanying 0.22% to 6.04% of AAAs.⁷ Retrograde flow associated with it may cause left to right shunting and venous congestion, leading to exacerbation of heart failure and impaired renal function.^6,8,9 In some cases, both residual ACF and T2E are self-limiting and do not require treatment.^3,10 This can occur if there is high resistance in the aneurysm sac, resulting in the loss of reverse flow in the collaterals.¹¹ In our case, the IMA communicating with a low pressure IVC reduced the pressure in the sac—promoting persistent T2E.¹¹ Intervention was carried out because of the heart failure and acute kidney injury in this patient, in addition to concerns of impending bowel ischemia caused by left to right shunt in the IMA.^4,5 Considering the patient’s comorbidities, we decided to perform T2E embolization, with the aim of secondary ACF closure, as reported in several cases.^12,13 This approach is preferred especially when the endoleak involves a single supply vessel and has lower mortality and less complications than open ACF repair.^14–17 In our case, it reduced the flow through the fistula between the IVC and IMA, eventually leading to its closure.

There are limited data on long-term outcomes and lack of evidence to guide specific management of ACF.¹⁴ A conservative approach may be chosen in asymptomatic disease, given no complications or sac expansion,¹⁰ but prophylactic intervention may be advised in case of a large shunt to prevent hemodynamic sequalae.¹⁴ According to the European Society for Vascular Surgery clinical guidelines, the follow-up plan for this patient includes an annual DUS and CTA every 5 years. If there is reduction in sac diameter > 1 cm, the DUS will be abandoned. On the other hand, if there is an increase in the sac size of > 1 cm, reintervention will be considered based on up-to-date CTA findings.¹⁸