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INTRODUCTION
The Onyx liquid embolic agent (ethylene vinyl alcohol copolymer; Covidien/ev3, Irvine, CA, USA) is a permanent, non-adhesive polymer for the management of vascular malformations. Onyx has been well established in recent years as a very important material in the treatment of arteriovenous malformations (AVMs). The angiographic cure rate of AVM using Onyx varies from 20% to 94.1%.1)10)13)21) When using the Onyx, it is essential to wait for the creation of a plug around the tip of the catheter, which enables the effective forward penetration of Onyx. However, proper creation of the plug is difficult as it can be a time-consuming and unpredictable process.
Recent reports show that the introduction of dimethyl sulfoxide (DMSO)-compatible dual-lumen balloon microcatheters improves the efficiency of AVM embolization.8)12) In this article, we present our initial experiences with transarterial balloon-assisted Onyx embolization of intracranial AVMs using the dual-lumen balloon microcatheter.
CASE REPORT
Case 1
A 49-year-old man was admitted to the Neurosurgery Department in our hospital a few hours after experiencing sudden severe dizziness and mental deterioration. He denied any history of hypertension or diabetes. His family and medical histories were non-contributory. On neurological examination, he was drowsy but had no focal neurological deficits. A non-contrast-enhanced computed tomography (CT) head scan showed diffuse subarachnoid hemorrhages (SAHs) in the basal cisterns and large intraventricular hemorrhages (IVHs) throughout the ventricles (Fig. 1A). The ventricles were also enlarged. Three-dimensional CT angiography and conventional cerebral angiography showed an AVM in the left lower frontal region, which was supplied by the left frontopolar artery and drained by the ventricular vein to the sigmoid sinus via the straight and transverse sinuses (Fig. 1B and Fig. 1C). The single drainage vein showed severe ectasia, tortuosity, and a varix, which was suspected to have ruptured (Fig. 1C).
First, we performed extraventricular drainage to relieve the acute hydrocephalus. As the angiography revealed a single feeder (left frontopolar artery) with a diameter of about 3 mm, we planned to perform balloon-assisted Onyx embolization. We performed AVM embolization using 2.8 mL of Onyx assisted by the Scepter XC balloon (Microvention, Inc., Tustin, California, USA) of 4 × 10 mm in size. The duration of the procedure was 20 minutes and it was successful, i.e. the nidus of the AVM was totally occluded (Fig. 2). After the procedure, the patient was managed conservatively. Three weeks after the hemorrhages, the patient showed mild memory impairment and was referred to the rehabilitation department. At two months after the hemorrhages, a non-contrast-enhanced CT head scan showed no abnormal findings (Fig. 3A) and the patient showed signs of improvement in memory. Seven months after the hemorrhages cerebral angiography revealed that the AVM nidus remained totally occluded (Fig. 3B).
Case 2
A 37-year-old man was admitted to the neurosurgery department in our hospital a few hours after experiencing sudden syncope. He denied any history of hypertension or diabetes. His family and medical histories were non-contributory. On neurological examination, he was alert and did not show any focal neurological deficits. A non-contrast-enhanced CT head scan showed mild hyperdense lesions at the right medial frontal base (Fig. 4A). Brain magnetic resonance imaging (MRI) and angiography (MRA) and conventional cerebral angiography showed an AVM at the right frontal pole, which was supplied by the right medial orbitofrontal and frontopolar arteries and drained by the superficial cerebral vein to the superior sagittal sinus (Fig. 4B, C).
As the angiography revealed that the diameter of the feeder vessel was about 2 mm, we planned to perform balloon-assisted Onyx embolization. One of the feeder vessels, the right medial orbitofrontal artery, was very tortuous (Fig. 5A); the exchange technique was therefore used. This involved the introduction of a 45-degree preshaped Echelon 010 microcatheter into the right medial orbitofrontal artery close to the AVM nidus. A Transcend 014 300 cm microwire was inserted into the Echelon 010 microcatheter and the Echelon microcatheter was withdrawn, leaving the Transcend microwire in situ. The Scepter XC balloon was then introduced into the right medial orbitofrontal artery along the Transcend 014 300 cm microwire. Endovascular embolization of the right medial orbitofrontal artery was performed using 2.8 mL of Onyx assisted by the Scepter XC balloon (4 × 10 mm). The duration of the procedure was 30 minutes and it was successful, i.e. the lower two thirds of the AVM nidus was occluded (Fig. 5A). Angiography of the right frontopolar artery revealed that the upper one third of the AVM remained, and that the artery was also very tortuous. (Fig. 5A). We used the same equipment and exchange technique, with which the Scepter XC balloon was introduced into the right frontopolar artery at the region close to the residual AVM nidus. Endovascular embolization of this artery was performed using 1.3 ml of Onyx assisted by the Scepter XC balloon (4 × 10 mm). The procedure lasted 15 minutes and was successful with the nidus of AVM being totally occluded (Fig. 5B). After the procedure, the patient was managed conservatively and was discharged uneventfully several days later.
DISCUSSION
In recent years, the Onyx system has been used extensively for AVM embolization with an improved rate of angiographic occlusion. When using the Onyx, it is important to wait for the creation of a plug around the tip of the catheter because the plug allows the forward flow of the Onyx.21) The plug is formed through the reflux of Onyx at the tip of the catheter and it may require time for proper plug formation because Onyx penetration is very variable. If unintended reflux occurs, the Onyx injection should be stopped for 1-2 minutes, prolonging the procedure time. Unintended early reflux is one of the main causes of incomplete AVM embolization and one of the causes of some complications such as cerebral infarction due to reflux of the liquid to proximal normal branches,20) stuck microcatheters that could not be removed and arterial rupture during the catheter removal procedures.21)
In our cases, the Scepter XC balloon microcatheter acted as a plug making it possible to accomplish immediate forward flow of Onyx. Because there was no reflux of Onyx, we improved the angiographic embolization rate of AVM without the proximal branch occlusion or stuck microcatheters. Arrest of blood due to the Scepter XC balloon microcatheter allowed us to control the Onyx penetration rate more precisely and allowed us to protect the early occlusion of drainage veins. As a result, it took a shorter time than that done without Scepter SC balloon microcatheter to perform the AVM embolization, and total occlusion of AVMs was obtained without any complications.
Initially a detachable balloon was used as the permanent embolic device.3)9)14)17)18)19) Thereafter, a single-lumen balloon-assisted embolization using Onyx was used for dural AVF.2)6)11)15)16) They applied a single-lumen balloon microcatheter followed by a conventional DMSO compatible microcatheter (proximal balloon and distal microcatheter) into the feeding artery and performed the ballooning of a single-lumen balloon microcatheter followed by Onyx injection via the DMSO compatible microcatheter, during which the microcatheter was jailed against the vessel wall. This jailing technique might not completely prevent Onyx reflux. With the advent of the dual-lumen balloon microcatheter, dual-lumen balloon-assisted embolization using Onyx has been used for dural AVF4)5) and for extracranial AVMs.7)12)
Recently, dual-lumen balloon-assisted embolization using Onyx has also been used for intracranial AVMs.8) In Jagadeesan's report, embolization using Onyx was performed in four intracranial AVMs.8) In all cases there was immediate antegrade flow and adequate penetration of Onyx with satisfactory angiographic occlusion rates. In one case, however, arterial rupture occurred and this was successfully managed using balloon, Onyx infusion, and surgical removal of the hemorrhage. The authors emphasized the importance of paying strict attention to matching the balloon inflation to the size of the vessel on the roadmap, as well as designation of one operator to balloon inflation and deflation throughout the procedure.
In both our cases, there was immediate forward flow and adequate penetration of Onyx and complete angiographic cures were achieved. There were no ischemic or hemorrhagic complications. However, there were some difficulties in the procedures. The most important factor was the navigation of the dual-lumen balloon microcatheter to the appropriate position of the feeding artery. Usually feeding arteries are relatively wide, but become tortuous in the AVM. The experience in our cases was similar. The lumens of A3 size were about 2-3 mm but they were very tortuous, which made navigation of the dual-lumen balloon microcatheter difficult. We overcame the difficulty by using microcatheter microwire exchange techniques as described above. Although we succeeded with this technique, it is not always possible. Therefore, when planning dual-lumen balloon-assisted embolization, it is very important to assess the route of the vessel to determine the type of technique to use. Another difficulty is rupture of the balloon. In order to prevent this complication, we matched the balloon inflation to the size of the vessel on the roadmap. We experienced no ruptures in our cases.
CONCLUSION
In keeping with other cases reported in the literature, we successfully performed transarterial Onyx embolization of intracranial AVMs using DMSO compatible dual-lumen balloon microcatheters. In the procedure of Onyx embolization for AVMs, reflux of Onyx is central. The Scepter XC balloon microcatheter acted as a plug, which enables immediate forward flow and penetration of Onyx without issues of reflux. It may also reduce the procedure time and increase the rate of angiographic occlusion. Navigation of the dual-lumen balloon microcatheter, however, remains challenging.
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