Microcatheter entrapment retrieval from Onyx embolization in brain arteriovenous malformations: A technical note

Abstract

Objective

Many techniques have been use for retrieval of an entrapped microcatheter during Onyx (eV3 Neurovascular) embolization of brain arteriovenous malformations (BAVMs). We report our technique that we term “pull-push-pull” that can be utilized as first management in retrieving the microcatheter.

Method

We analyzed a total of 37 patients that underwent BAVM embolization with either Onyx 18 or 34 at our institution. Standard embolization techniques were utilized with the use of Marathon (eV3 Neurovascular) microcatheter. When difficulty in retrieving the microcatheter arose, we used the “pull-push-pull” technique. The technique comprises the eV3 protocol of retraction. In addition, the microcatheter is stretched causing the Onyx cast to stretch in its inner core, creating a more thorough cohesive property amongst the Onyx mixture. Then the microcatheter is pushed back and to its point of embolization origin. Afterwards, retraction of the microcatheter is enabled as it can be easily dislodged from the cast. Multiple attempts can be repeated as needed.

Result and discussion

We had three patients that had difficulty with removal of microcatheter (8.1%). Utilization of the “pull-push-pull” technique was used on two of those patients. No neurological complication was observed with our technique. We believe the cohesive property of Onyx solution helps in the retrieval of the catheter by our method and technique.

Conclusion

We believe the “pull-push-pull” can be utilized and be an additional technique before attempting other catheter retrieval techniques in Onyx BAVM embolization.

Introduction

Reduction of brain arteriovenous malformation (BAVM) size and blood flow is the desired outcome of embolization before becoming more amenable for microsurgical resection.^1–3 Many different agents of embolization have been utilized in the past, e.g. iso-butyl 2-cyanoacrylate and N-butyl-cyanoarcylate (NBCA), that are suboptimal in surgical characteristics in terms of increased vessel pliability and shortened amount of time needed for proper embolization.^3,4 However, Onyx (eV3 Neurovascular; Irvine, California, USA) is a liquid polymerizing embolic agent that, according to some data, provides more time, better penetration, and obliteration of the arteriovenous malformation (AVM) nidus than NBCA.^3–5 It is a pre-mixed, radiopaque fluid consisting of ethylene-vinyl alcohol copolymer (EVOH), dimethyl sulfoxide solvent (DMSO), and micronized tantalum powder.^1,6

However, utilizing Onyx also has its own risks such as hemorrhagic rupture of the vessels, angiotoxicity due to DMSO, reflux to normal vessels and, in particular, difficulty in removal and entrapment of the microcatheter.^6–8 Certain factors are associated with an increased risk in catheter retention like prolonged injection time of the solution, tortuosity of the blood vessels, increase in injection time, and large amount of reflux along the microcatheter tip.⁹ Retrieval of the retained microcatheter can be daunting and many techniques have been ascribed in managing this complication like the “over-the-catheter” and the “monorail snare” technique.^7,10,11

In this paper, we would like to add the “pull-push-pull” technique to the repository of management techniques of an entrapped microcatheter after Onyx embolization. Our experiences with this novel technique in BAVM embolization have been favorable and cost-effective. Our technique can be described as a modified technique that “pushes” the microcatheter into the most proximal point of the Onyx cast after following the eV3 protocol in catheter retraction. This allows for the catheter to break off at the initial site of Onyx cast embolization and better retrieval of the entrapped catheter. We then slowly pull on the catheter in an effort at retrieving the catheter again. Attempting our technique can reduce the need for resection of the catheter at the femoral artery or adding additional equipment into a patient’s blood vessel.

Methods

Onyx is supplied in ready-to-use vials of different concentration of EVOH copolymer, 6.0 and 8.0% (Onyx 18 and 34 respectively). The lower the concentration of the copolymer the less viscous the agent is, which corresponds to better distal penetration of the BAVM nidus.^1,6,12 The characteristic of Onyx is like a “lava flow”, i.e. precipitation occurs upon contact with blood solution. This forms a spongy polymeric cast from the outside wall of the blood vessel leaving the liquid center to continue to flow. Additionally, Onyx is more cohesive than adhesive which is a unique characteristic compared with previous embolization solutions. Generally, Onyx 18 is used on a plexiform nidus while Onyx 34 is used on large arteriovenous shunts in the AVM.¹

From January 2010–November 2013, we analyzed a total of 37 patients for treatment of BAVMs at the Medical Center of Central Georgia in the Neuroendovascular Suite with biplane vascular digital subtraction angiography. Informed consent was obtained from all patients and the risks and benefits of the procedure were thoroughly explained. Briefly, the procedure was performed by a standard transfemoral catheterization approach for access into the BAVMs. Angiographic contrast and imaging were utilized for proper AVM nidus visualization. A DMSO-compatible microcatheter (Marathon, eV3) was inserted at the nidus with confirmation from microcatheter angiography. The approach to Onyx injection was by the “plug and push” technique for embolization of the AVMs.

Even while utilizing eV3 standard protocol for retraction, three patients had difficulties with prolonged catheter retrieval time and retention (8.1%). On the initial occurrence with this difficulty, we were concerned with the lodged catheter due to prolonged time (>90 min) with sequential gentle traction. A decision was made in the best interest of the patient’s safety by cutting the distal microcatheter at the entry point into the femoral artery using the standard protocol for an entrapped catheter. In two similar cases like these first occurrences, catheter retraction was tried and failed. However, on our second patient with entrapped catheter, retrieval of the catheter was possible when we pushed the microcatheter into its original position and retracted it. A similar technique was used for the last patient with multiple attempts tried and final resolution of entrapped catheter was achieved.

As illustrated in Figure 1, the microcatheter tip is placed as close to the AVM nidus as possible to ensure Onyx embolization and occlusion. After embolization is completed, we slowly and incrementally (centimeter by centimeter), withdraw the microcatheter. Tension will be increased as more traction is applied translating this energy towards the end of the microcatheter tip. Usually, sustained moderate tension will release the microcatheter from the Onyx cast and withdrawal of the microcatheter can be completed. However, if the tip is still entrapped in the Onyx cast and repetitive retraction tension is applied without release, the pull-push-pull technique can be applied. The first step has already been applied with regular retractions. This will stretch the Onyx cast from inside out as one pulls. Next, the microcatheter is displaced back into its proximal origin of embolization by passively releasing of tension of the catheter or actively pushing it back a few millimeters. One can then pull or retracted the microcatheter again with moderate tension. Several attempts can be repeated by pulling and pushing and pulling. After driving the microcatheter into the Onyx cast, appropriate withdrawal of the catheter will dislodge the microcatheter from the cast.

Figure 1.

Pull-push-pull technique. (a) After Onyx embolization, gentle retraction is applied to the Marathon microcatheter. Usually, retrieval of the catheter can be achieved at this point but if there is reflux of Onyx, the catheter can be entrapped. (b) Continue gentle retraction as one would with regular retrieval and notice the stretching of the Onyx solution. This will increase the surface area thereby promoting more cohesive properties of the Onyx cast. (c) Push the tip towards the original site of embolization and back a few millimeters into the proximal cast. (d) One can then pull/retract the catheter with improved catheter retrieval. Repeat the steps as necessary.

Results and discussion

We experienced three patients with difficulties of catheter entrapment with BAVM embolization. Two of the patients had removal of the microcatheter by our technique with one still having a retained catheter when we utilized the recommended eV3 protocol. For the patient with the catheter still retained through the femoral artery, that patient was put on anticoagulant regimen with further follow-up on the surgical resection of the BAVM. One and six months follow-up showed no further neurological complications in all three patients.

There are many ways of retrieving an entrapped catheter. For instance, the “monorail snare” technique uses an Amplatz 4 mm gooseneck microsnare combined with an Excelsior 1018 microcatheter driving over the entrapped Marathon microcatheter towards it distal end as far as possible. After tightly closing the loop of the gooseneck microsnare at the distal end, the microsnare and the Excelsior microcatheter are pulled back with the ensnared Marathon. This technique is highly effective and was reported back with great success for catheter entrapment.¹⁰ Another technique was the “over-the-catheter” technique which utilizes another catheter that is placed over the trapped microcatheter. In that study, the author used an Outreach distal access catheter, putting it over the Marathon microcatheter, and positioned adjacently to the proximal cast. Using the Outreach catheter as a counterforce, the entrapped catheter can be pulled out with relative ease.⁷ Finally, a detachable microcatheter tip has been used outside the USA and has been successful in preventing entrapment.⁹

We feel that our technique could be added to the repertoire on managing an entrapped catheter. The benefits from using our technique is that it does not require an additional catheter or wiring that could potentially complicate retrieving such a microcatheter. Complications such as hemorrhagic rupture of the BAVM feeding vessels, inducing a thromboembolic event, causing a vasospasm, catheter breakage, and stroke are a major consideration with entrapment.^7,10,11,13 Additionally, our technique could be an initial trial before using other techniques to retrieve the microcatheter. Furthermore, our technique closely resembles the eV3 protocol for retrieval of the microcatheter by slow sustained retraction. It is only at the end that we added that crucial step to release the catheter.

We hypothesize that the reason why retracting the microcatheter causes it to release from the Onyx cast is because of Onyx's unique cohesive property. By stretching the microcatheter proximally, the inner cast of Onyx is still “liquefied” which causes the Onyx cast to stretch along the catheter as retraction is applied. This creates more surface area for Onyx to cohere to itself and less adherence to the microcatheter. Likewise, once we start to push the microcatheter back to its origin and a few millimeters beyond the proximal cast, we are utilizing the cohesive property of Onyx to bind to itself and leave the microcatheter loosen enough to extract it from the cast. To make this explanation simpler, one can make an analogy to pulling weeds in a garden. From experience, if one keeps on pulling the weed, one could break the weed at its base and leaving the root still underground. However, if one pulls the weed without breaking it and then pushes the weed back to the dirt and finally pulling it again, it is easier to extract the whole weed plant.

Conclusion

Onyx is widely used as an agent of embolization of BAVMs and study has shown it is as effective as prior agent such as NBCA.³ However, Onyx is known to cause retention of the microcatheter due to reflux of the solution, length of injection time, and tortuosity. Hence, there are many techniques in managing the retrieval of the microcatheter. We have described a unique technique that can be termed as “pull-push-pull” that has promising potential in that it can be an initial management technique in retrieving the catheter before necessitating additional catheters and wires. We did not observe any adverse neurological outcomes in our patients; however, we only have experience of two patients with this complication using this technique. Like other management techniques of retrieval, one still must expect and be prepared for adverse effects. In our limited experience, we feel that it is safe, cost effective, and an approachable first step in dealing with entrapped catheter of Onyx embolization.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this technical note.

Funding

The authors received no financial support for the research, authorship, and/or publication of this technical note.