A Review of Treatment for Type II Endoleak after Endovascular Abdominal Aortic Aneurysm Repair

Abstract

Type II endoleak is the most common complication after endovascular abdominal aortic aneurysm repair. Type II endoleak with aneurysm sac growth is not benign for long-term outcomes of endovascular abdominal aortic aneurysm repair and should be treated to prevent secondary stent graft-related complications and aneurysm rupture. The current consensus is to consider treatments for persistent type II endoleak with significant aneurysm sac growth. For complete embolization of type II endoleak to obliterate the endoleak cavity with the elimination of all supplying arteries, it is necessary to select and combine the treatment options. Although the treatment techniques for type II endoleak have advanced, clinical outcomes remain unsatisfactory. To overcome this clinical discrepancy, the optimal patient-tailored treatment strategy is required in clinical practice, with an understanding of the current status and limitations of treatment for type II endoleak.

Introduction

Type II endoleak (T2EL) is defined as persistent retrograde collateral blood flow from the aortic side branches within an abdominal aortic aneurysm (AAA) sac outside the stent graft after endovascular abdominal aortic aneurysm repair (EVAR). T2EL is the most common complication and has been reported to occur from the inferior mesenteric artery (IMA), lumbar arteries (LAs), or median sacral artery (MSA) in 10%-30% of patients during follow-up after EVAR [1-7]. In general, the prognosis of T2ELs is considered benign, and the majority of them resolve spontaneously [7-9].

However, it is currently accepted that T2ELs associated with aneurysm sac growth are not benign. Patients with persistent T2EL beyond six months require lifelong surveillance after EVAR. Natural history studies have shown that 10% to 40% of patients with persistent T2EL result in aneurysm sac growth [3, 4, 9]. Furthermore, they have a high incidence of requiring more secondary interventions and conversion to open surgery, and aneurysm sac rupture [7]. Aneurysm sac growth due to T2EL can cause proximal and distal landing zone shortening, which may lead to secondary stent graft-related complications such as type I endoleak (T1EL), type III endoleak (T3EL), or stent graft migration [10-13]. There is no controversy that T1EL and T3EL are associated with aneurysm rupture and require immediate treatments. Furthermore, persistent T2EL with aneurysm sac growth is a small but independent risk factor for late aneurysm rupture [4, 7].

To prevent secondary stent graft-related complications and late aneurysm rupture, persistent T2EL with aneurysm sac growth should require optimal treatments. Therefore, redefining the current status and limitations of treatment for T2EL is essential for the optimal management after EVAR in clinical practice. The objective of this review is to provide the readers with help in the decision-making process on this topic.

Indications of Treatment for Type II Endoleak

Management of T2EL after EVAR depends on the associated risk of aneurysm rupture. Guidelines recommend conservative management with imaging follow-up for T2ELs with a shrinking or stable aneurysm sac. Overall, 30%-50% of T2ELs after EVAR will resolve spontaneously without treatment [7, 14]. Although the optimal timing of treatment for T2ELs remains controversial, the current consensus is to consider treatment for persistent T2EL with significant aneurysm sac growth or with the onset of symptoms attributable to the endoleak [15-20]. The Society for Vascular Surgery guidelines recommend treatment for persistent T2EL with aneurysm sac growth >5 mm [21]. In contrast, the European Society for Vascular Surgery guidelines recommend treatment for persistent T2EL with aneurysm sac growth >10 mm [22]. To certify “significant” aneurysm sac growth, the aneurysm sac diameter should be measured using the same imaging modality.

The early advantages of EVAR compared to surgery are lost over time due to complications including T2EL [23]. Furthermore, the clinical efficacy of initial successful treatments for T2EL also appears to be lost over time due to the recurrent and residual T2ELs [7, 10, 24-26]. Therefore, the indication for treatment of T2EL should be redefined for better long-term outcomes after EVAR.

In addition to T2EL, anatomical characteristics outside the instructions for use of EVAR including hostile necks were independently associated with aneurysmal sac growth after EVAR [27]. Hostile necks for EVAR are also risk factors for T1EL [28-30]. Numerous studies have demonstrated increased risks of late aneurysm rupture after EVAR [7, 11-13, 31, 32]. Large aneurysm sac size was associated with an increased risk of late aneurysm rupture [13, 31, 32] and was a significant predictor of aneurysm sac growth after embolization for T2EL [24, 25]. To improve the durability and longevity of EVAR, it is necessary to prevent secondary stent graft-related complications and aneurysm rupture. Patients with large aneurysm sac size and/or hostile necks cannot tolerate the “significant” aneurysm sac growth with T2EL [26]. When considering indications for treatment, it might be necessary to evaluate not only the aneurysm sac growth but also the anatomical characteristics including aneurysm sac size and proximal and distal necks.

The majority of patients recommended for EVAR are frail and elderly [26], and significant aneurysm sac growth with T2EL is often detected with long-term follow-up [3, 4, 9, 22]. If frail and elderly patients result in aneurysm sac growth several years after EVAR, highly invasive procedures such as open surgical conversion would no longer be feasible for them. Therefore, more aggressive treatment seems reasonable for persistent T2EL without significant aneurysm sac growth in patients with a high risk of secondary stent graft-related complications and aneurysm rupture at the time of original EVAR. They may be suitable candidates for preemptive embolization of the aortic side branches to prevent T2EL following EVAR [33]. A comprehensive strategy after EVAR should be individualized for each patient to optimize the timing and methods of treatment for T2EL depending on patient characteristics as well as the anatomical risk factors (Fig. 1).

Figure 1.

The author's suggested a strategy for management of type II endoleak.

The current consensus is to consider treatment of persistent type II endoleak with significant aneurysm sac growth. For patients with hostile necks and large aneurysm sac size at high risk for secondary stent graft-related complications and aneurysm rupture, treatment of type II endoleak may be considered with or without aneurysm sac growth.

It is important to rule out an occult T1EL or T3EL which are concurrent with T2ELs before procedures. Aneurysm sac growth in the presence of a suspected T2EL can result from an occult T1EL or T3EL [15, 34]. If conventional CT angiography is inconclusive, transarterial angiography or Time-resolved CT angiography can be useful in identifying the source of the endoleak [35-37]. These imaging techniques with visualization of the supplying collateral arteries are also helpful in planning treatment for T2EL [36, 37].

Options of Treatment for Type II Endoleak

Currently, several treatment options have been proposed for T2EL. Of these, embolization is the first line of treatment [15-19]. In cases where embolization fails or is not technically feasible, surgical treatment is commonly recommended. Surgical treatment options include laparoscopic, robotic, or open aortic side branch ligation, aneurysm sac plication, or total or partial stent graft explantation [38-42]. Antiplatelet therapy is associated with recurrent or residual T2ELs after embolization [43-45], and endoleaks were more common in patients with anticoagulation therapy after EVAR [46]. Antiplatelet and anticoagulant therapies are associated with aneurysm sac growth after EVAR [47, 48]. The efficacy of antifibrinolytic therapy with tranexamic acid therapy to prevent recurrent and residual T2EL has not been proven [49].

T2EL can be categorized into type IIa endoleak with a single supplying artery and type IIb endoleak (T2bEL) with multiple supplying arteries [17]. T2bEL can be particularly technically challenging and often requires multiple procedures [50]. Embolization of only the aortic side branch outside the endoleak cavity is ineffective, and collateral T2ELs can be recurrent over time [51, 52]. Although it has been reported that embolization of the endoleak cavity alone is not inferior to embolization of the endoleak cavity and aortic side branches [53], incomplete embolization of the endoleak cavity alone may also result in recurrence of collateral T2ELs. Complex T2bEL with an endoleak cavity and multiple supplying arteries have similar clinical characteristics to AVM with nidus and multiple inflow and outflow vessels. Treatment for AVM cannot be successful unless the nidus is completely obliterated [52]. Therefore, the technical goal of embolization for T2EL is the complete obliteration of the endoleak cavity with the elimination of all supplying arteries required to prevent recurrence [7, 15-20, 51, 54].

Transarterial, direct percutaneous puncture, transcaval, and perigraft approaches for embolization have been reported [15-20]. The selection of the approach and technique for embolization depends on the anatomical findings of the preoperative CT angiography. The most feasible and safest approach for each patient to access the endoleak cavity should be the priority.

Transarterial approach

The most common technique for T2EL is transarterial embolization, which involves catheterization of the endoleak cavity via the supplying collateral arteries [15-20, 55-57]. It is essential to advance a microcatheter through the retrograde collateral arteries to the endoleak cavity within the aneurysm sac. The transarterial approach is most effective for T2EL from IMA. The common retrograde collateral pathway to IMA is from superior mesenteric artery (SMA) via the middle colic artery, the arc of Riolan or marginal artery of Drummond, and the left colic artery. While its pathway is long and tortuous, the diameter of the arteries is relatively larger. In contrast, the typical retrograde collateral pathway to LA or MSA, the supplying artery of T2EL, is from the iliolumbar artery (ILA) via smaller and extremely tortuous collateral vessels. Transarterial embolization of T2EL from LA or MSA is technically more challenging than from IMA.

The transarterial approach using the double coaxial microcatheter technique can be successfully performed with high rates [25, 58, 59]. To advance a 1.9-F non-tapered microcatheter coaxially through a 2.7-F microcatheter to the endoleak cavity via the long and tortuous collateral pathway, stable access should be achieved with a guiding sheath and/or a catheter advanced to SMA or ILA (Fig. 2). A high-flow steerable microcatheter has been reported to be useful as the double microcatheter technique for challenging catheterization [60-62]. Cannulation with a microcatheter through the endoleak cavity to other patent aortic side branches is feasible.

Figure 2.

An 80-year-old man presented with persistent type II endoleak with aneurysm sac growth after EVAR.

Preoperative CT angiography showed the endoleak cavity (arrow) from lumbar arteries (LAs) and median sacral artery (MSA) without type I or III endoleak (a). After successful catheterization of the endoleak cavity from the iliolumbar artery via the left 4th LA using transarterial approach with the double coaxial microcatheter technique, an angiography showed the endoleak cavity and all supplying arteries (b). A diagnostic angiogram and saccogram, to rule out the other possible source of endoleak was performed through a 1.9-F non-tapered microcatheter after selective embolization of the right 4th LA with coils (c). After successful embolization with N-butyl cyanoacrylate (NBCA) glue (arrowhead) from the endoleak cavity to the ostium of LAs and MSA, additional embolization of the left 4th LA was performed with coils. The competition angiography showed no endoleak (d). Postoperative CT showed the endoleak cavity filled with NBCA glue (arrowhead) (e). The aneurysm sac enlarged significantly with washout of NBCA glue in three years after successful embolization (f), and CT angiography revealed type Ib endoleak (g).

Direct percutaneous puncture approach

Percutaneous puncture of the aneurysm sac can allow direct access to the endoleak cavity within the aneurysm sac [15-20, 63-65]. Preoperative CT angiography is closely evaluated to plan an optimal puncture route to the endoleak cavity avoiding larger vessels and organs. Percutaneous puncture is typically performed via a translumbar approach with prone positioning. Patients are required to keep positioning and resting.

A sheath needle is advanced percutaneously under image guidance through the aneurysm sac into the endoleak cavity. CT, come-beam CT, fluoroscopy, or ultrasound guidance have been reported for the direct percutaneous puncture approach [63-69]. After the needle tip achieves the endoleak cavity, a diagnostic angiogram, saccogram, is performed via the needle to confirm the endoleak cavity and supplying collateral arteries. It is possible to embolize the supplying arteries through the endoleak cavity with a microcatheter similarly to the transarterial approach with the coaxial technique [66]. The direct approach to the endoleak cavity by percutaneous puncture can reduce fluoroscopy time, total procedure time, and iodine contrast material dose compared to the transarterial approach [67].

Although the translumbar approach is useful for accessing the posterolateral endoleak cavity, it can be difficult to access the endoleak cavity anterior to the stent graft. Furthermore, prone positioning is often poorly tolerated in elderly and/or unstable patients. The transabdominal approach can be an alternative if the translumbar approach is not feasible [68, 69].

Transcaval approach

The transcaval approach technique is an alternative to the transarterial and direct percutaneous puncture approaches if they fail or are not technically feasible. This technique provides direct access to the endoleak cavity within the AAA sac via the inferior vena cava (IVC) with a sheathed needle [15-20, 70, 71]. It is useful for T2EL with a posterior endoleak cavity close to IVC. An angled sheathed needle is wedged against the IVC wall adjacent to the endoleak cavity using a combination of landmarks, fluoroscopic imaging, and intravascular ultrasound. After a successful puncture to penetrate the IVC and AAA sac wall, a catheter is advanced through the sheath for subsequent embolization. However, the transcaval approach is more challenging to cannulate the supplying collateral arteries through the endoleak cavity due to its limited puncture angle.

Perigraft approach

The perigraft approach is also an adjunctive technique when other techniques have failed to achieve the endoleak cavity. A catheter and guidewire are advanced through the gap between the iliac limb of the stent graft and the iliac arterial wall, navigating through the aneurysm sac thrombus into the endoleak cavity [16-18, 72, 73]. It is useful for T2EL with the endoleak cavity in the terminal aorta. The incidence of subsequent type Ib endoleak should be ruled out after the procedure.

Embolization materials

Embolization techniques are performed using coils and liquid embolization agents such as N-butyl cyanoacrylate (NBCA), Ethylene vinyl alcohol copolymer (Onyx), etc [16-20, 24, 74-76]. Coils are usually reserved for selective embolization of the aortic branches. Coil embolization alone has been reported to require more secondary reinterventions [24]. T2EL with aneurysm sac growth treated with liquid embolization agents were less likely to require further reinterventions than those treated with coils [74]. When selective embolization of all supplying arteries is not technically feasible, the adjunctive administration of liquid embolization agents is recommended. Liquid embolization agents can spread from the injection site to allow embolization of the smaller outflow branches through the endoleak cavity without catheter cannulation [24, 75, 76]. To achieve complete obliteration of the endoleak cavity and elimination of all supplying arteries, embolization materials should be selected and combined based on the angiographic findings.

There is no consensus on the optimal embolization material or combination of embolization materials for T2EL [24-26, 51]. Several studies have reported on alternative liquid embolization materials for T2EL. NBCA-lipiodol-ethanol mixture (NLE) is less likely to adhere than NBCA-lipiodol mixture. Embolization with NLE might be more effective than with NBCA glue in the short term [77]. Initial experiences with other new non-adhesive liquid embolization materials and injectable biocompatible elastomers for T2EL have been reported [49, 78, 79].

Outcomes of Treatment for Type II Endoleak

There is insufficient evidence on the comparison of treatment techniques to determine which one is the most effective [7, 10, 15, 18, 67]. It is necessary to be cautious in the interpretation of outcome data due to the heterogeneous technical feasibility, potential refractoriness to treatment, and follow-up duration after treatment for T2EL.

Previous studies have reported various definitions of technical and clinical success [7, 10, 67]. Although the definition of technical success is often not stated, technical success is commonly defined as no evidence of residual endoleak within the aneurysmal sac at the completion of the procedure. In addition, the successful reduction of the aneurysm sac pressure or deployment of embolization materials into the endoleak cavity is also defined as technical success. Furthermore, there are several definitions of clinical endpoints, including the recurrence of T2EL, aneurysm sac growth, reintervention, and aneurysm rupture. These unclear definitions of treatment endpoints also contribute to the lack of consensus on the efficacy of treatment for T2EL.

The methods and timing of surveillance after successful treatment for T2EL are controversial and the indication criteria of reintervention for the recurrence of T2EL have also not been established. The angiogram during procedures might be limited in detecting the residual T2EL due to poor spatial resolution with two-dimensional imaging [25]. The significant streak artifact on CT imaging due to embolization materials after treatment may make it difficult to evaluate the residual or recurrent endoleaks after embolization [80]. Even after successful treatment for T2EL continued surveillance and close follow-up are important. In clinical practice, it is essential to define the optimal patient-tailored endpoints to assess clinical benefits. The clinical goal of treatment for T2EL should be balanced with the life expectancy.

Technical success

The systematic reviews and meta-analyses of the outcomes of treatment for T2EL following EVAR showed high technical success rates for all techniques. The overall technical success rates ranged from 60% to 90% [7, 10, 67]. The technical success rates were 84.0%, 98.7%, and 93.3% for transarterial, translumbar, and transcaval approach, respectively [10]. The translumbar approach has higher technical success rates than the transarterial approach because it allows direct access to the endoleak cavity [67]. However, there is no consensus to recommend a particular treatment for T2EL [16, 17]. The selection of the embolization approach and technique should be dependent on the anatomical findings of T2EL, cost-effectiveness, and operator experience [16, 17, 81].

Clinical success

The systematic reviews and meta-analyses showed the overall clinical success was 68.4% [7, 10]. Although the currently available techniques have high technical success rates, technical success does not translate into clinical success. Regardless of technique or outcomes of treatment, recurrence of T2EL on follow-up imaging was confirmed in one-third of patients after treatment. In addition, one-third of those patients resulted in subsequent aneurysm sac growth in short-term follow-up [7, 10]. In mid-term and long-term follow-up, more than half of the patients after treatment had a recurrence of T2EL. At three years after initial treatment for T2EL, 50%-70% of patients after treatment resulted in subsequent aneurysm sac growth >5 mm, and 20%-65% of patients required subsequent reinterventions [24-26]. Patients who underwent treatment for T2EL had a relatively frequent need for additional subsequent reinterventions [24]. Although aneurysm rupture after treatment for T2EL was extremely rare, 5%-20% of patients required surgical explant following treatment for T2EL [24-26]. Although the aneurysm rupture after EVAR with T2EL is rare [7], several studies have shown treatments for T2EL neither improved survival nor aneurysm-related mortality compared to the conservative approach after EVAR [82-84].

Unfortunately, the clinical efficacy of initial successful treatments for T2EL appears to be lost over time due to recurrent or residual T2ELs. The discrepancy between technical and clinical success rates might be due to occult T2EL that cannot be detected on the competition angiography of the embolization procedure [25]. Otherwise, the recanalization of embolized or thrombosed branches and reperfusion from collateral branches such as vasa vasorum might also result in recurrent T2EL [85]. In particular, T2EL associated with vasa vasorum would be extremely refractory to management with embolization [26]. The pathophysiology of refractory T2EL is not fully understood, and therefore future studies should be required to improve the clinical outcomes.

Complications

The systematic review and meta-analysis reported perioperative complications following treatment of T2EL occurred in 3.8% of patients, and aneurysm-related mortality was 1.8% [10]. Major complications associated with treatment for T2EL are rare.

Non-target embolization potentially occurring with liquid embolization agents has been commonly reported. This complication includes pulmonary embolism, ischemic colitis, ischemic lumbar plexopathy, acute lower limb claudication, and deep vein thrombosis [17]. Pulmonary embolism and deep vein thrombosis may occur with transcaval or percutaneous translumbar approach via IVC [71, 86]. Ischemic colitis may occur secondary to embolization of IMA [87]. Ischemic lumbar plexopathy or acute lower limb claudication may occur with liquid embolization materials after embolization from the distal lumbar artery before achieving the endoleak cavity [17, 88, 89].

Infection of the stent graft or aneurysm sac after embolization is an uncommon and serious complication. The embolization techniques with a direct percutaneous puncture approach carry a risk of postoperative infection [90, 91]. The transarterial or transcaval approach reduces the risk of infection compared to translumbar embolization [92].

Summary and Future Consideration

T2EL is the most common complication after EVAR. T2EL with aneurysm sac growth after EVAR is not benign for the long-term outcomes of EVAR and should be treated to prevent secondary stent graft-related complications and aneurysm rupture. There is no consensus on the optimal embolization technique or material for T2EL, and it is, therefore, necessary to select and combine the treatment options to obliterate the endoleak cavity with the elimination of all supplying arteries. Although the treatment techniques for T2EL have advanced, the clinical outcomes remain unsatisfactory. To overcome this clinical discrepancy, the optimal patient-tailored treatment strategy is required in clinical practice.

Future studies should investigate the optimal management for T2EL and the pathophysiology of refractory T2EL to refine indications, procedural details, and clinical outcomes.

Conflict of Interest

None

Author Contribution

H.H.: original draft, conceptualization, review, and editing.