Outcome and technical evolution of type 2 endoleak embolization with ethylene-vinyl-alcohol copolymer

Abstract

Purpose

This study aims to evaluate the safety and efficacy of novel approaches to type 2 endoleak access for the purpose of embolization using ethylene-vinyl-alcohol copolymer (EVOH) in patients with abdominal aortic aneurysm (AAA) sac expansion post endovascular abdominal aortic repair (EVAR).

Methods

A retrospective review of 43 consecutive patients (mean age = 80.2 ± 6.7 years) who underwent 52 embolization procedures for type 2 endoleaks using EVOH was performed at a single institution. Catheterization of the endoleaks was achieved using the transarterial (TA) and direct translumbar approaches (DTL), in addition to the novel direct transabdominal (DTA) and perigraft (PG) approaches. Endpoints included technical success of endoleak catheterization, technical success of endoleak embolization, endoleak persistence, endoleak recurrence, AAA sac area change, and adverse events.

Results

The TA, DTL, DTA, and PG approaches were used 25, 2, 14, and 19 times respectively, including nine procedures where a combination of approaches was used. The technical success rate of endoleak embolization was 98%. Five patients developed recurrent type 2 endoleaks, while five patients developed a type 1 endoleak. The persistent endoleak rate at a mean initial follow-up of 3 months was 34%. At a mean follow-up of 18 months, 58% of patients demonstrated absence of an endoleak, and 71% showed freedom from AAA sac enlargement. No major adverse events were recorded.

Conclusion

The DTA and PG approaches were safe and effective in this cohort of patients undergoing embolization of type 2 endoleaks with EVOH.

Keywords

Abdominal aortic aneurysm endovascular aortic repair endoleak type 2 embolization EVOH onyx

Introduction

Although the management of persistent type 2 endoleaks has been controversial in terms of both timing and technique, most practitioners reserve secondary interventions for cases involving aneurysm growth of greater than 5 mm within a 6-month period.¹ Several studies have demonstrated that successful eradication of the endoleak requires embolization of the nidus with a liquid embolic such as ethylene-vinyl-alcohol copolymer (EVOH), with or without adjunctive coil embolization of feeding branches.^2–9

The most common techniques for catheterization of the endoleak nidus are the translumbar approach and the modified transarterial approach, both of which carry limitations.^10–13 With the translumbar approach, the ability to target the endoleak in real-time is limited when using a fluoroscopic approach, and additional catheter and wire manipulation may be required to catheterize the endoleak within the aneurysm sac. Computed tomography (CT) guidance helps target the endoleak but is cumbersome because it requires patient transfer. Communicating lumbar arteries are usually not accessible from a translumbar approach because of the posteroanterior orientation of the needle, thus increasing the risk of non-target embolization when using a liquid embolic. Further, the prone positioning required for the translumbar approach may be poorly tolerated in elderly patients and does not lend itself to concurrent transfemoral access. The modified transarterial approach is effective for catheterization of endoleaks arising from the inferior mesenteric artery (IMA). However, catheterization of the lumbar arteries and other non-IMA sources of endoleaks is time-consuming and carries a suboptimal technical success rate.

Alternative approaches have been described to address these limitations including the transcaval approach,^14,15 transabdominal approach,^16–20 and perigraft approach.^21–23 The purpose of the current study was to review the evolution of the transabdominal and perigraft approaches to endoleak access in our practice and analyze their relative effectiveness and safety with respect to EVOH embolization of type 2 endoleaks.

Methods

Study design and patient population

This Health Insurance Probability and Accountability Act (HIPAA)–compliant retrospective cohort study was approved by the institutional review board, and informed consent was waived. A retrospective chart and imaging review of consecutive patients who underwent embolization of type 2 endoleaks with EVOH was performed at a single institution between January 2009 and February 2018. Forty-three patients were enrolled in the study. Patient demographics are detailed in Table 1. All patients demonstrated AAA aneurysm sac expansion of ≥ 5 mm in maximal diameter in a 6-month period on cross-sectional imaging prior to intervention.

Table 1.

Demographics.

Characteristic	N = 43
Age (years)	80.2 ± 6.69
Male	32 (74.4%)
History of smoking	28 (65.1%)
Diabetes	12 (27.9%)
Transient ischemic attack	5 (11.6%)
Stroke	5 (11.6%)
Coronary artery disease	30 (69.8%)
Peripheral vascular disease	5 (11.6%)
Hypercholesterolemia	36 (81.4%)
Chronic heart failure	5 (11.6%)
Chronic obstructive pulmonary disease	11 (25.6%)
Atrial fibrillation	7 (16.3%)
Single antiplatelet therapy	38 (88.4%)
Dual antiplatelet therapy	10 (23.3%)
Anticoagulation	11 (25.6%)

All procedures were performed by three board-certified interventional radiologists with 13, 18, and 20 years of experience, respectively. The approach to endoleak catheterization was dependent on its location and source. Techniques for endoleak catheterization were divided into three categories: transarterial, direct, and perigraft approaches.

Transarterial approach

The modified transarterial (TA) approach has been previously described by Stavropoulos et al.¹⁰ Briefly, a common femoral artery access was used to perform retrograde transcollateral catheterization of the endoleak channel via the feeding branch using a microcatheter. The most common feeding vessels catheterized with this approach were the inferior mesenteric artery (IMA) via the superior mesenteric artery (SMA) and lumbar arteries (LA) via the internal iliac artery.

Direct approach

The direct approach was divided into two subcategories: the direct translumbar (DTL) approach and the direct transabdominal (DTA) approach. The DTL approach involved percutaneous translumbar access into the AAA sac under CT guidance in prone positioning using a 19-gauge sheathed needle (Cook, Bloomington, IN) from a left paraspinal approach. Following access, patients were transferred to the angiography suite for embolization.

The DTA approach was selected if an anterior transabdominal window to the AAA sac, free of the intervening bowel, was identified on cross-sectional imaging. Ultrasound guidance with color-flow imaging was utilized to visualize the endoleak and target it with a 21G needle. Exchange was then made for a 4F or 5F catheter to complete the embolization (Figure 1).

Figure 1.

(a) Axial CT angiogram demonstrating type 2 endoleak along the posterior aspect of the AAA. (b) Ultrasound image during ultrasound-guided direct anterior transabdominal (DTA) access of the endoleak. The needle (solid arrow) is visualized between the endograft limbs tracking toward the type 2 endoleak seen on color doppler (dashed arrow).

Perigraft approach

The perigraft approach (PG) was essentially a hybrid of the TA and direct approaches where common femoral artery access was obtained followed by direct catheterization of the AAA sac by undermining the iliac limb of the endograft with an angled support catheter and guidewire and advancing the catheter into the aneurysm sac between the endograft and arterial wall. After AAA sac access was gained, the catheter and guidewire were used to catheterize the endoleak based on correlation with prior cross-sectional imaging. Exchange for different-shaped catheters, sheaths, and guidewires was made as needed to facilitate catheterization of the endoleak (Figure 2).

Figure 2.

(a) Digital subtraction angiogram of lumbar endoleak via the perigraft approach (PG) with opacification of communicating lumbar arteries (solid arrows). (b) Spot fluoroscopic image post embolization of type 2 endoleak with EVOH extruding into the culprit lumbar artery (dashed arrow).

Regardless of approach, after access to the endoleak was confirmed by pulsatile blood return, digital subtraction angiography (DSA) was performed to assess for communicating arteries and correlate the endoleak morphology with cross-sectional imaging. In some cases, additional communicating arteries were able to be identified and targeted beyond the information of the pre-operative CT angiogram. EVOH (Onyx-18/34; Medtronic, Minneapolis, MN) was then instilled into the endoleak nidus via a DMSO-compatible microcatheter (Renegade, Boston Scientific, Marlborough, MA; Progreat, Terumo, Tokyo, Japan) with the goal of replacing the space occupied by the endoleak with an EVOH cast while, ideally, allowing EVOH to extrude into communicating branches. Typically, higher viscosity Onyx-34 (8% EVOH/92% DMSO; Medtronic) was used initially to limit non-target embolization, while Onyx-18 (6% EVOH/94% DMSO) was used as an endoleak filler. Additional coil embolization was performed as needed to reduce the amount of EVOH required and to embolize branch vessels in order to prevent non-target embolization. Multiple approaches were employed if necessary to achieve complete and safe embolization of the endoleak. Technical success of endoleak catheterization was analyzed by each approach. Technical success of embolization was defined as endoleak embolization without residual endoleak on completion angiography.

Follow-up CT or magnetic resonance imaging (MRI) examinations were scheduled at 3, 6, 12, and 24 months, and reviewed for persistence and recurrence of endoleaks and change in aneurysm size. Persistence was defined as presence of a type 2 endoleak on the first follow-up cross-sectional exam. Recurrence was defined as any endoleak identified during follow-up after initial negative cross-sectional imaging. Both pre- and post-procedural cross-sectional imaging studies were used to measure the maximal transaxial area of the AAA using the formula for the area of an ellipse (A): A = πab where a and b represent the long and short axis radius measurements, respectively, of the aneurysm on cross-sectional imaging at the level of maximal dilation. Changes in the aneurysm sac area were defined as decreased (reduction in area greater than 5 cm²), increased (enlargement of area greater than 5 cm²), or stable (changes smaller than 5 cm²) when compared with the most recent pre-interventional cross-sectional examination. Procedural and post-procedural adverse events were recorded according to the SIR reporting standards.²⁴

Statistical analysis

Descriptive statistics included calculated means, standard deviations, and medians. All calculations were performed using Microsoft Excel (version 16.12; Microsoft Corporation, Redmond, Washington).

Results

Mean time from EVAR to the index embolization procedure was 46.6 ± 38.0 months. The cohort included 34 complex endoleaks where more than one communicating branch was visualized angiographically. Communicating branches to the type 2 endoleaks are listed in Table 2. Eight of the 43 patients underwent repeat embolization procedures, including one patient who underwent two repeat procedures, resulting in a total of 52 embolization procedures. Eight reinterventions were performed for persistent or recurrent type 2 endoleaks in the setting of enlarging AAAs or those measuring greater than 6 cm in diameter. A mean number of 3.1 ± 2.7 vials of Onyx-18 and 2.2 ± 1.5 vials of Onyx-34 were used per procedure. Adjunctive coil embolization, using platinum Interlock (Boston Scientific, Marlborough, MA), Ruby (Penumbra, Alameda, CA), and/or Nester (Cook, Bloomington, IN) coils was performed in 27 procedures. There was one technical failure of embolization in which the endoleak was still visualized at completion angiography, resulting in a technical success rate of embolization of 98%.

Table 2.

Branch vessel involvement.

Vessel	N = 111
Right L1	0 (0%)
Right L2	4 (3.6%)
Right L3	18 (16.2%)
Right L4	16 (14.4%)
Right L5	5 (4.5%)
Left L1	0 (0%)
Left L2	4 (3.6%)
Left L3	17 (15.3%)
Left L4	15 (13.5%)
Left L5	4 (3.6%)
IMA	17 (15.3%)
Accessory renal	6 (5.4%)
Median sacral	3 (2.7%)
Internal iliac	2 (1.8%)

There were nine procedures in which multiple approaches were used successfully, including one procedure of two separate TA approaches (lumbar and IMA), two procedures of combined TA and PG approaches, and six procedures of combined TA and DTA approaches. The TA, DTL, DTA, and PG approaches were used successfully in 25, 2, 14, and 19 procedures, respectively. The TA approach was technically successful in 25 of 33 attempts (76%), including 14 of 14 (100%) for the IMA and 11 of 19 (58%) for lumbar arteries. The direct approach (DTA and DTL) was successful in all 16 attempted procedures (100%). The perigraft access was successful in 19 of 22 attempts (86%). In one patient, a transcaval approach was employed to successfully embolize an endoleak that was inaccessible with the PG approach. Technical success of catheterization by approach is summarized in Table 3.

Table 3.

Technical success of endoleak catheterization by approach.

	Attempts	Catheterized	Technical success rate (%)
Transarterial—IMA	14	14	100
Transarterial—lumbar	19	11	58
Direct translumbar	2	2	100
Direct transabdominal	14	14	100
Transcaval	1	1	100
Perigraft	22	19	86
TOTAL	72	61	85

Five patients were lost to follow-up. Mean follow-up in the remaining patients was 18 ± 17 months. The initial post-procedural CT/MRI was performed at a mean follow-up of 3 ± 6 months and demonstrated absence of an endoleak in 31 of 47 procedures (66%). Persistent type 2 endoleaks were identified in the 16 (34%) remaining procedures, of which six demonstrated an accompanying increase in native sac size, while 10 demonstrated stability or decrease in sac size. There were five procedures that demonstrated a recurrent type 2 endoleak during follow-up (mean 15 ± 9 months from index procedure) only one of which was associated with a size increase of the AAA. Five patients (11%) developed a type 1 endoleak during follow-up (mean: 26 ± 19 months from index procedure), consisting of one type 1B and four type 1A endoleaks, including two graft migrations. The type 1B and 1 type 1A endoleaks were treated by graft extension, while two of the type 1A endoleaks were repaired by proximal extension with snorkel. Two of the four type 1A leaks presented with a ruptured AAA but without hemodynamic instability. Results are summarized by procedure and approach in Table 4.

Table 4.

Results by approach for all procedures (N = 52).

	N	No follow-up	Technical success of embolization	Persistent type 2 endoleak	Freedom from sac enlargement	Development of type 1 endoleak	Recurrent type 2 endoleak
Transarterial—IMA	8	2	8	1	5	1	0
Transarterial—lumbar	6	0	6	3	4	1	0
Direct translumbar	2	0	2	0	1	0	0
Direct transabdominal	8	2	7	2	2	1	2
Transcaval	1	0	1	0	1	0	0
Perigraft	18	1	18	8	13	2	2
Combination	9	0	9	2	7	0	1
TOTAL (%)^a	52	5	51	16 (34)	33(71)	5 (11)	5 (11)

At a mean follow-up of 18 months, 58% (22 of 38) of patients demonstrated absence of a persistent or recurrent type 1 or 2 endoleak and 71% (27 of 38) of patients showed stability (± 5 cm²) or decrease (> 5 cm²) in the aneurysm sac area (Table 5). No major adverse events were recorded.

Table 5.

Leak and size results by patient (N = 43).

	N = 38^a	%	Re-intervened	% Re-intervened
Leak—Increase	4	11	1	25
Leak—Decrease/Stable	7	18	1	14
No leak—Increase	2	5	0	0
No leak—Decrease/Stable	20	53	3	15
Type 1 endoleak	5	13	3	60

Discussion

The outcome of type 2 endoleak embolization reported in this study, with a persistent endoleak rate of 34%, is similar to other studies using contemporary embolization techniques and EVOH.^2,5,10,13,21 More importantly, 71% of the patients demonstrated stable or decreased aneurysm areas at a mean follow-up of 18 months. Two patients demonstrated absence of a type 2 endoleak on follow-up with associated increase in the AAA area. We postulated these to be related to the presence of a type 5 endoleak versus increased size related to the volume of EVOH instilled into the sac during the embolization procedure.

Of the 43 patients in this cohort, five developed type 1 endoleaks during follow-up with two of those presenting as ruptured AAAs. None of the type 1 endoleaks occurred at the site of previous PG approach, including the sole type 1B endoleak. All type 1A endoleaks occurred as a result of proximal neck degeneration, with or without graft migration, in patients with enlarging and/or large (> 6 cm) aneurysms. It is unclear why we experienced such a high rate (11%) of type 1 endoleaks in this cohort compared with other studies. It is possible that other studies under-reported type 1 endoleaks because they are frequently obscured by artifacts from embolic materials such as coils or possible misinterpretation of recurrences as type 2 endoleaks. Nonetheless, it is important to note that the two patients with type 1 endoleaks and AAA rupture did not present with hemodynamic instability. In any event, the risk of type 1 endoleak development in patients with type 2 endoleaks highlights the need for aggressive management of type 2 endoleaks in the setting of an enlarging AAA or a large aneurysm sac, as postulated by Massis et al.²¹

The widely used lumbar TA and DTL approaches for catheterizing the endoleak nidus are time-consuming and carry significant limitations. In order to overcome these limitations, we have embraced alternative approaches to endoleak catheterization in our practice and striven to treat all type 2 endoleaks in the supine position in expedient fashion. We were able to achieve this by replacing the TA lumbar artery and DTL approaches with the PG and DTA approaches. This strategy proved successful over the course of the study with all lumbar TA and DTL attempts occurring early in our experience. There was only one procedure in which we were forced to resort to a transcaval approach in order to complete the embolization procedure. By abandoning the DTL approach, all the techniques used can be performed on a supine patient. As such, concurrent use of different approaches is feasible, as was the case in nine patients in this cohort. In the majority of these cases, a second access is employed to prevent non-target embolization of the liquid embolic. We consider this to be a major advantage of avoiding the DTL approach and performing the procedure in a supine position.

The DTA approach is particularly potent when combined with color-flow US imaging guidance because it allows access to the endoleak within the aneurysm sac directly with a micropuncture needle, thus eliminating the need to search within the sac for the endoleak source, which may be time-consuming or unfeasible. However, the DTA approach is only possible in a minority of patients, as it requires the existence of an anterior transabdominal window free of the intervening bowel and blood vessels. The effectiveness of the DTA approach has been demonstrated in a recent study.²⁰

Unlike the DTA approach, the PG approach is feasible in the majority of patients, including those without incomplete apposition of the endograft to the iliac arterial wall. As with its first description by Massis et al.,²¹ we found the PG approach to be remarkably effective, with a high technical success rate and low complication rate. Similar to Massis et al.,²¹ we did not encounter occurrences of type 1B endoleaks as a result of the PG approach. The major limitation of the PG approach is that the endoleak is not targeted directly under imaging guidance as with the DTA approach. Therefore, catheter and wire exchanges may be required to locate the endoleak within the AAA since the point of entry into the aneurysm sac with the PG approach is arbitrary, similar to the fluoroscopically guided DTL and transcaval approaches. Nevertheless, in our experience, the majority of PG approaches were successfully completed with just a 4F support catheter and hydrophilic guidewire. We found the PG approach particularly useful in endoleaks arising from lumbar arteries, with 18 of our 19 perigraft approaches performed for lumbar artery endoleaks. As such, we were able to abandon the suboptimal lumbar artery TA approach over the course of our experience. The TA IMA approach remains part of our algorithm since it is straightforward and essentially successful in all procedures (100% in our cohort).

One of the major limitations we encountered to the follow-up management of endoleaks treated with EVOH is the problem of artifacts on CT scans related to the radiopaque tantalum powder in the EVOH, making it virtually impossible to evaluate for residual endoleaks in some of these patients. MRI is a validated technique for the surveillance of endografts post EVAR.^25–27 During the course of this study, we discovered the strength of MRI for post-embolization follow-up imaging of endoleaks, where there is minimal artifact caused by the EVOH (Figure 3). For the same reason, we use only platinum coils to perform adjunctive coil embolization, as platinum causes less susceptibility artifacts than steel coils on MRI. It is also important to note a cost differential between coils and EVOH with EVOH costing approximately US$1000/mL and coils ranging from approximately US$500–1000 per coil, depending on coil type.

Figure 3.

(a) CT angiogram with significant streak artifact from prior EVOH (solid arrow) with poorly visualized persistent type 2 endoleak posteriorly (dashed arrow). (b) Axial contrast-enhanced volumetric interpolated breath-hold examination (VIBE) MR image depicting prior EVOH anteriorly (solid arrow) with persistent type 2 endoleak posteriorly (dashed arrow). (c) Endoleak angiogram and (d) spot fluoroscopic image during embolization of persistent posterior type 2 endoleak (dashed arrows). (e) Follow-up axial contrast-enhanced VIBE MRI image demonstrating EVOH in both the anterior (solid arrow) and posterior (dashed arrow) components of the type 2 endoleak.

Limitations of our study include the retrospective design, small sample size, and incomplete follow-up. The small sample size further divided into the smaller individual approach groups prevented a statistically meaningful comparison of these groups. We also have a very limited experience with the DTL approach, thus introducing bias into the study toward the more novel alternatives. This may be partially a result of our using CT guidance for the translumbar puncture, making the procedure particularly cumbersome because it requires patient transfer from CT to angiography. We recognize that several studies have demonstrated the feasibility of fluoroscopic-guided translumbar puncture, which is less cumbersome but still has the other aforementioned limitations inherent to the approach. These could possibly be overcome by using cone-beam CT-guided translumbar access, but this was not evaluated in this study. Additionally, other advanced techniques for endoleak embolization such as transcaval^14,15 and transgraft²⁸ approaches were incompletely assessed or not included in this analysis, respectively.

In conclusion, the DTA and PG approaches to endoleak catheterization were safe and effective in this cohort of patients undergoing embolization of type 2 endoleaks with EVOH. These novel techniques address some of the limitations of the DTA and lumbar artery TA approaches and appear complementary to other existing approaches. With 1/3 of patients demonstrating persistent endoleaks post-intervention, consistent with prior studies, close follow-up with serial imaging is critical regardless of approach.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Daniel A Leung

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