Predictive Factors and Strategies to Prevent the Development of Type 2 Endoleaks following Endovascular Aneurysm Repair

Abstract

Type 2 endoleaks are a potential complication of endovascular aortic repair for abdominal aortic aneurysms. They are caused by vessels that have been excluded from the aorta lumen, but may still fill the aneurysm sac due to collateral filling. Type 2 endoleaks may lead to increased morbidity and need for additional procedures. Being able to identify patients at risk for Type 2 endoleaks and prevent them is important for any physician who is performing endovascular aortic repair.

An abdominal aortic aneurysm (AAA) is a dilatation of the aortic diameter to greater than 3 cm due to weakening of the endoluminal wall. ¹ Pressure within the AAA sac will cause progressive widening and, if left untreated, eventual rupture. ¹ AAA rupture has a high mortality rate, up to 80% in some studies, and results in 175,000 deaths around the world, including 1% of deaths for men older than 65 years. ^{1 2} Elective repair of the AAA, whether by an open or endovascular approach, has been shown to reduce mortality from this entity exponentially. ³ Long-term survival is comparable between patients who undergo endovascular versus open repair with better perioperative mortality in patients undergoing endovascular repair, although some studies have suggested trends toward slightly better long-term survival after endovascular aortic repair (EVAR). ^{3 4 5 6} A point of contention when comparing EVAR to open repair is the need for secondary procedures postrepair, with some studies finding more secondary procedures post-EVAR and others finding no significant difference. ^{3 5} These secondary procedures can include procedures to correct an endoleak. The purpose of this article is to briefly review the different types of endoleaks post-EVAR, with a specific focus on Type 2 endoleaks, factors related to the development of Type 2 endoleak, and potential endovascular techniques that can be employed to prevent Type 2 endoleaks post-EVAR.

Presentation of Endoleak after Endovascular Aneurysm Repair

An endoleak is a potential complication after aortic aneurysm repair related due to incomplete treatment characterized by leakage into the aneurysm sac postprocedure. ^{7 8 9} The classification system for endoleaks identifies five different types of endoleaks. ^{7 8 9} A Type 1 endoleak is due to poor apposition of the stent graft with one of the sites of the native artery, either proximally (Type 1A) or distally (Type 1B), which allows for leakage around the stent graft and into the aneurysm sac. ^{8 9} A Type 2 endoleak is due to retrograde blood flow through an arterial branch that is excluded by the graft but opens into the AAA sac. ^{8 9} Type 2 endoleaks are the most common form of endoleak after EVAR. ^{8 9} Type 3 endoleaks are related to graft failure, leading to direct spillage into the aneurysm sac of blood product. ^{8 9} A Type 4 endoleak is typically related to graft porosity, but are normally seen transiently during the intraoperative setting and then resolve. ^{8 9} Type 5 endoleaks are those that result in sac enlargement without an obvious source of the endoleak and are likely secondary to endotension. ^{8 9}

Predictive Factors Related to Incidence of Type 2 Endoleak

Any extra procedures post-EVAR increase patient cost and potential morbidity from complications. ⁵ As a result, it is important to identify which patients are most at risk to develop a Type 2 endoleak so that it can be treated either prior to or during the EVAR procedure. Type 2 endoleaks can be seen in up to 25% of patients depending on the study and are caused by retrograde blood flow into branch vessels that arise from the excluded portions of the aneurysm sac. ^{10 11} The most common arteries involved in Type 2 endoleaks are the inferior mesenteric artery (IMA) and lumbar artery branches, although there are also reports in the literature of accessory renal arteries causing them as well. ^{10 11 12} Type 2A endoleaks are secondary to one vessel, while Type 2B endoleaks are secondary to two or more vessels. ¹¹ The major preoperative risk factors for the development of Type 2 endoleaks are related to patient anatomy; so, factors like number of patent lumbar arteries, a patent IMA, or patent accessory renal arteries, in addition to aneurysm sac size, have been correlated with increased incidence of Type 2 endoleaks. ^{11 13} During the EVAR procedure, operators need to be aware that if a Type 2 endoleak can be seen for greater than 6 seconds on angiography, the patient will likely present with a Type 2 endoleak on postprocedural imaging. ^{11 14} Hypogastric artery embolization prior to or during EVAR procedure and distal graft extension were also associated with increased rates of Type 2 endoleak. ¹⁵ Patient factors such as cigarette smoking, advanced age, and the presence of cancer can be associated with decreased rates of postprocedure Type 2 endoleaks. ^{11 15} Conversely, the presence of certain anticoagulation medication is shown to have an increased rates Type 2 endoleaks, which may indicate that the patient's ability to form clot is related to the presentation of Type 2 endoleaks. ^{11 16}

Strategies and Techniques to Prevent Development of Type 2 Endoleak

It is a well-established technique that embolizing vessels that may potentially cause a Type 2 endoleak, such as the IMA, lumbar arteries, or accessory renal arteries, can reduce the incidence of Type 2 endoleak in the postoperative course. ^{12 17 18 19} Preoperative embolization has shown reduced need for follow-up procedures, improved morbidity, and decreased chance of aneurysm sac size enlargement. ^{17 18 19}

In performing EVAR, computed tomography angiography (CTA) is a useful preprocedure tool for assessing aneurysm sac size and identifying arteries for potential side branch embolization ( Fig. 1 ). ¹⁷ CTA is often employed for evaluating endoleaks postprocedurally, and comparison to preoperative imaging will allow for comparisons in aneurysm sac size between pre- and postprocedure values, confirming the presence of an endoleak as well as the success or failure of preoperative embolization. ^{8 9 17}

Fig. 1.

Selected CT angiographic images of a 58-year old man obtained to assess the patient's AAA and plan for patient's EVAR procedure. Images are ordered from superior to inferior. Accessory renal arteries (arrows) are identified bilaterally ( a, b ). The IMAs (arrows) are identified traversing originating inferiorly and traversing superiorly through the thrombosed aneurysm sac ( c, d ). The patient would subsequently go on to preoperative embolization of both accessory renal arteries and the IMA ( Figs. 2 – 4 ). AAA, abdominal aortic aneurysm; IMA, inferior mesenteric artery; EVAR, endovascular aortic repair.

On CTA assessment of the IMA, certain factors can be assessed to determine if the patient is more likely to have a Type 2 endoleak from this artery including diameter greater than 2.5 mm and lack of calcification, stenosis, or mural thrombus at the IMA origin. ²⁰ IMA embolization has been demonstrated to be cost neutral due to prevention of repeat procedures, and can lead to a reduction in overall aneurysm sac diameter compared with those patients who do not receive IMA embolization. ²¹ Coils are a commonly used embolic agent for this procedure. ^{17 22} IMA embolization is generally considered to be a safe procedure, with most patients having no evidence of complications. ¹⁷ The most common complication is nonlocalized abdominal pain, which resolves with supportive management. ¹⁷ While a potential for mesenteric ischemia does exist, most patients are well collateralized from the superior mesenteric artery via the arc of Riolan and the arc of Drummond. ¹⁷ Fig. 2 demonstrates the utility of IMA embolization.

Fig. 2.

The IMA has been cannulated with a 5-Fr Sos catheter (AngioDynamics, Latham, NY) with subsequent angiography performed ( a ). A microcatheter was advanced through the IMA and 0.018 interlock coils (Boston Scientific, Marlborough, MA) were deployed prior to the IMA branching point. Postdeployment angiography demonstrates significantly reduced flow to the distal branches of the IMA with most of the contrast being retained proximal to the deployed coils ( b ). IMA, inferior mesenteric artery.

Accessory renal arteries are an anatomic variation that leads to multiple vessels supplying the kidneys. ^{12 18} Exclusion of the accessory renal arteries has not been shown to cause significant worsening of renal function postprocedurally due to preservation of the main renal artery, although small renal infarcts may be identified ( Fig. 3b ). ^{12 18} Accessory renal arteries with diameters larger than 3 mm are more prone to result in Type 2 endoleaks. ¹² When deciding to embolize these patients, it is important to identify main renal artery supply angiographically to ensure the appropriate vessel is being selected. Figs. 3 to 5 demonstrate renal artery embolization pre–endograft placement.

Fig. 3.

The main left renal artery ( a ) and accessory left renal artery ( b ) were cannulated with a 5-Fr Sos catheter (AngioDynamics, Latham, NY). Differentiation was made based on how much parenchyma was supplied by each artery; limited parenchymal enhancement of the lower pole was identified from the left accessory renal artery ( b ). 0.018 interlock coils (Boston Scientific, Marlborough, MA) were subsequently deployed into the left accessory renal artery, with significantly reduced flow seen on postdeployment angiography ( c ).

Fig. 5.

Aortography performed during patient's EVAR procedure, 2 weeks after preoperative embolization. Planning aortogram ( a ) shows coil embolization material in the bilateral renal arteries with no evidence of filling of the bilateral accessory renal arteries and IMA. Post-EVAR deployment aortogram ( b ) does not show evidence of Type 2 endoleak. IMA, inferior mesenteric artery; EVAR, endovascular aortic repair.

Fig. 4.

The main right renal artery ( a ) and accessory right renal artery ( b ) were cannulated with a 5-Fr JR4 guide catheter (Merit Medical, South Jordan, UT). Most of the renal parenchyma enhances from the main renal artery ( a ), with some lower pole enhancement noted from the accessory right renal artery ( b ). After deployment of 0.018 interlock coils (Boston Scientific, Marlborough, MA), angiography demonstrates reduced flow through the artery, with most of the contrast being seen proximal to the coils ( c ).

Fig. 6.

Delayed axial CT angiographic images of the patient 1 month post-EVAR. Coil embolization material is noted in the bilateral accessory renal arteries ( a ) and IMA ( c ). Small renal infarcts are noted in the lower poles of the bilateral kidneys ( b ), with normal parenchymal enhancement otherwise and no change in patient's baseline renal function. There is no evidence of contrast within the thrombosed aneurysm sac to suggest any endoleak ( b - d ). Distal branches of the IMA that supply the left hemicolon are seen to be opacified, due to filling of collateral branches from superior mesenteric artery (SMA) supply. Patient has had follow-up for over 2 years without evidence of endoleak, has seen slight reduction in aneurysm sac size, and no need for secondary procedures. IMA, inferior mesenteric artery; EVAR, endovascular aortic repair

Lumbar arterial branches may be too small to identify on CTA to warrant significant consideration with regard to preoperative embolization. ¹⁷ However, if large enough, lumbar arteries are a common artery that can lead to Type 2 endoleak. ¹⁹ Lumbar arteries with diameters larger than 2 mm are more likely to lead to Type 2 endoleaks. ²² Preoperative coil embolization of lumbar artery branches can reduce incidence of Type 2 endoleak in these patients. ²²

Other techniques to prevent Type 2 endoleaks that can be performed intraoperatively are described in the literature. Direct injection of the aneurysm sac with thrombin appears to be an additional safe procedure that reduces incidence of Type 2 endoleaks. ²³ Another potential maneuver is the use of an endovascular sealant device at the time of EVAR placement, which has had positive results in reducing rates of Type 1 and Type 2 endoleaks. ²⁴

Conclusion

Type 2 endoleaks have historically been a common complication of EVAR for AAA. Their presence can potentially increase the morbidity of the patient and cost of patient care due to the requirement of follow-up procedures to treat them. Preoperative embolization of arterial branches that could cause Type 2 endoleaks is safe and can reduce the incidence of Type 2 endoleaks in these patients.