Long-term results of intra-arterial onyx injection for type II endoleaks following endovascular aneurysm repair

Introduction

Type II endoleaks are the commonest cause of continued sac perfusion following endovascular aneurysm repair (EVAR) of infrarenal abdominal aortic aneurysms. Although many type II endoleaks will thrombose spontaneously or have limited effect on aneurysm growth, in some cases, they may provoke continued aneurysm expansion and possible rupture.^1,2 These warrant treatment. There are a number of methods documented to treat persistent type II endoleaks. The liquid embolic agent Onyx (eV3 Endovascular, Irvine, CA) is an ethylene vinyl alcohol copolymer dissolved in dimethyl sulfoxide (DMSO) and mixed with micronized tantalum powder (for visualization under fluoroscopy). Upon contact with blood, the material solidifies so that the flow of blood into the aneurysm is blocked.

Onyx liquid embolic system (LES) is a device approved by the FDA for the presurgical embolization of arteriovenous malformations (AVMs).^3,4 In later years, it has also been used for embolization of different types of endoleaks after endovascular aneurysm repair.

We report our experience of type II endoleak treatment after EVAR with intra-arterial injection of the embolizing liquid material, Onyx LES.

The aim of this paper is to document short- and long-term results up to five years to determine whether this treatment strategy is associated with long-term endoleak abolition and stabilization of sac growth.

Material and methods

From January 2005 to January 2012, we performed a retrospective review of a prospectively collected database of the last 600 patients, who underwent endovascular repair of an abdominal aortic aneurysm at our institution. During the follow-up, type II endoleaks were observed in 92 patients (15%).

Our standard indications for treatment are persistent, present for over three months, type II endoleaks with a growing aneurysm sac, more than 5 mm from the baseline measurement following stenting.

All procedures were performed in an interventional radiology suite, under local anaesthesia and sedation as appropriate. Embolizations were performed using percutaneous femoral transarterial approach in all 18 patients. The feeding vessel was accessed coaxially using a 5F catheter and microcatheter. The Onyx liquid embolic agent (18 and 34) was prepared in the same way in all patients. Onyx was shaken for 20 min, and then poured into the provided syringes. The embolic agent was injected through a compatible microcatheter. After the microcatheter had been located in the desired vessel, a small infusion of contrast through the microcatheter was performed to confirm proper positioning. The dead space of the micro catheter was then filled with DMSO, and then the Onyx was injected (Figures 1 to 3).

Onyx was the sole embolic agent used in all procedures. OPEN IN VIEWER

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Figure 2.

Anterior–posterior X-ray showing an embolized left lumbar branch with Onyx.

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Figure 3.

Digital subtraction angiography (DSA) showing type II endoleak, with retrograde filling of the aneurysm sac.

Our standard follow-up schedule includes postoperative clinical examination, computed tomography angiogram (CTA) before discharge and follow-up appointments at 6 and 12 months postoperatively and annually thereafter. No patient in this series was lost to follow-up. Mean follow-up was 19 (range 3–60) months.

Results

All patients in this group had persisting type II endoleak and aneurysm sac growth over 5 mm as the indication for treatment. Mean initial aneurysm sac size was 85.5 mm (range 55–120 mm).

Of the 92 patients with a type II endoleak identified, 36 patients required a secondary intervention to repair the type II endoleak, of which 18 patients were treated with intra-arterial injection of Onyx and included in the analysis.

Patient demographics and cardiovascular risk factors are reported in Table 1, including age, gender and comorbidity. There were 14 men and 4 women. Median age was 79 (range 67–86) years.

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Table 1.

Patient’s characteristics and comorbidities.

Onyx group, n  = 18	No. (%)
Age (years)	79 (67–86)
Gender (male/female)	14/4 (78%/22%)
Diabetes mellitus	4 (22%)
Hypertension	15 (83%)
Dyslipidaemia	7 (39%)
Smoking history	7 (39%)
Coronary artery disease	3 (17%)
Previous coronary intervention/cardiac surgery	2 (11%)
Renal impairment	2 (11%)
COPD	1 (5%)

The main feeding vessel of the endoleak was the internal iliac artery in seven cases, inferior mesenteric artery (IMA) in seven cases and L3 or L4 lumbar arteries in four cases (Figures 4 to 6). OPEN IN VIEWER

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Figure 5.

Angiogram showing type II endoleak, with retrograde filling of the aneurysm sac from a left ilio-lumbar artery. Coil is noted from previous intervention.

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Figure 6.

Digital subtraction angiography (DSA) revealing selective embolization of feeding branches using Onyx. Coil is noted from previous intervention.

Immediate technical success (considered as elimination of flow to the aneurysm sac) was achieved in all patients. There was no non-target embolization of Onyx material during procedures.

Mean in-hospital stay was 24 h. There was no mortality or morbidity associated to these procedures. There were no aneurysm-related complications.

During a mean follow-up of 19 months (range 3–60), actuarial survival was 100% at six months and one year.

Three patients had type II endoleaks identified on follow-up CTA examination, one at 6 and one at 12 months, but in a different location from the originally treated one. These patients are currently managed with close surveillance, with no increase in aneurysm sac size. The third patient presented with a new type II endoleak 24 months after the treatment. It was successfully treated with a new Onyx injection in the feeding branch of a lumbar artery. There were no other stent-graft-related complications or need for any further procedures.

Mean aneurysm diameter before the stent-graft implantation was 73.6 mm (range 55–100 mm). Mean aneurysms sac size before endoleak embolization with Onyx was 85.5 mm (range 55–120 mm).

Discussion

This report documents the long-term results of treatment of type II endoleaks with intra-arterial injections of Onyx in the lumbar, inferior and superior mesenteric, internal iliac arteries and their branches.

These are the most frequent type after EVAR, occurring after 10–25% of the cases of infrarenal EVAR.^1,2 They represent the most frequent complication after EVAR, before wound infection and local wound complications. ⁵ Examination of our series of EVAR procedures demonstrates a type II endoleak rate of 15%, in keeping with other publications.

The natural history of type II endoleaks is still debated. Some reports have related aneurysm rupture to type II endoleaks. Other studies have shown a benign course of type II endoleaks. ⁶

Given this controversial data, many authors perform selective treatment of type II endoleaks, depending on the persistence of the leak and aneurysmal sac growth.

Most of the recent series agree that small type II endoleaks detected on the immediate postoperative period can be managed with close surveillance, usually at 1, 6 and 12 months, with physical examination, duplex ultrasound and CT scan.^6–8

Around 40–70% of these type II leaks will spontaneously seal after a period of weeks or months.^6,7

There are certain cases where these endoleaks persist, with growth of the aneurysm sac. In those situations, there is a greater risk of complications, including aneurysm rupture and stent-graft migration.

The timing and most efficacious indication for treatment of type II endoleaks is still controversial in the literature. It is generally agreed that further interventions are not required, when the aneurysm sac decreases or remains stable. Most authors agree to treat those patients with persisting type II endoleaks, aneurysm growth or signs of bleeding.^1,2,6,8

Currently, there are different options for the treatment of these endoleaks, including endovascular procedures, laparoscopic and open surgical procedures. Open interventions are usually reserved for acute situations (rupture) or those infrequent cases of failure of endovascular interventions.

Endovascular approaches include treatment with embolization of the feeding vessels with different materials such as coils, gelfoams, thrombin, N-butyl cyanoacrylates, gel particles, microspheres, haemostatic agents and new agents such as Onyx.

The liquid embolic device Onyx was first used to treat vascular malformations, initially for intracranial AVMs.^3,4,9,10 Since then, around 80 articles have been published documenting the treatment of AVMs with Onyx.^3,4,9–13

A small number of series have been published regarding the treatment of type II endoleaks with Onyx.^14–18

The largest single-center experience of transarterial Onyx injection of 65 type II endoleaks, showed a 92.3% success rate. A decrease in aneurysm sac size was observed in 73.6% of patients. ¹⁴ Median follow-up was 15 weeks. Compared to our series, their study has a short follow-up time, which was only available for half of their patients. Martin et al. ¹⁷ and Abularrage et al. ¹⁶ have both presented their small series of type II endoleak following EVAR treated with Onyx injection with good results. These series demonstrate that Onyx is successful in ablating most feeding vessels, and aneurysm sac size did not increase in the short term.

All these series currently published have relatively short follow-up periods. The data in our paper include patients up to five years, with prolonged arterial blockage and no increase in sac size in any patient highlighting the long-term success of this treatment for type II endoleaks.

Our series of 18 patients showed successful exclusion of the endoleak in all treated patients in the two main expected territories of type II endoleak in the context of EVAR: the IMA and lumbar branches.

We believe that the key features that secure successful embolization with Onyx are homogenous filling of the embolization column and advancement of the liquid embolic as close to the sac as possible. The failure of one or both of these prerequisites could lead to failure of the embolization procedure. This could explain the relatively small failure rate reported in other series.

Onyx injection appears to be safe. In our series, there was no mortality or major morbidity associated to the Onyx embolization procedures. No complications secondary to puncture site were reported, and the patients were treated as day-cases in the majority. No complications secondary to the product delivery were detected.

Some limitations in the use of Onyx for the treatment of endoleaks include its relatively high cost as compared with other embolic agents, as well as the need of experienced hands for its use. Moreover, artefacts can be evident in postoperative CT angiograms, making it difficult to visualize small endoleaks. We use a combination of unenhanced and enhanced CT scan in the first postembolization scan to detect persistent endoleak.

There are conversely a number of advantages to its use. Compared to other embolic agents, the use of Onyx allows for embolization of smaller vessels, ensuring complete sealing of flow into the aneurysm sac and thereby prevents recanalization of the target vessel. Moreover, due to its high viscosity and handling features, Onyx may be administered at a slower and more controlled manner, without reflux to other branches, thus minimizing complications. Another advantage over other particles is that it can be clearly visualized due to its radiopacity. Moreover, Onyx only precipitates when contacting blood. This prevents easy blocking of the catheter, as happens with other particles such as cyanoacrylates.

In conclusion, our experience shows that the use of liquid embolic material, Onyx, is safe and seems to be effective in treating type II endoleaks over a significant time period. Successful treatment leads to arrest or regression of sac growth, although new type II endoleaks may still develop underlining the need for continued surveillance.