Dr. Chun and Prof. Morgan gave us a sneak peek at Prof. Morgan’s lecture “Embolisation with non-adhesive liquid embolic agent” for CIRSE 2022.
Embolisation with non-adhesive liquid embolic agent
Complex visceral artery aneurysms (VAA) may not be treatable with conventional techniques such as covered stenting or coil embolisation. These may exhibit a wide neck, arise at a major bifurcation or the parent artery must be preserved. In such cases, balloon-assisted embolisation with a non-adhesive liquid embolic agent may be a useful technique. These EVOH-based agents include Onyx™ (Medtronic, USA), Squid (Emboflu, Switzerland) and Precipitating Hydrophobic Injectable Liquid (PHIL) (Microvention, Terumo, Japan), developed primarily for use in intracranial aneurysms and vascular malformations. Onyx is the most widely used and discussed in more detail.
Onyx™ (Medtronic) is a cohesive liquid embolic agent, composed of ethylene-vinyl alcohol (EVOH) copolymer dissolved in dimethyl sulfoxide (DMSO) with suspended micronized tantalum powder. When the DMSO solvent diffuses away, Onyx forms a spongy elastic embolus. Onyx™ is supplied in ready-to-use vials and several formulations are available that differ in the concentration of copolymer and tantalum content (Figure 1). Onyx 34 (EVOH 8%) is more viscous and allows for more controlled injection in higher flow targets, whereas Onyx 18 (EVOH 6%) will travel more distally and penetrate deeper into the target lesion. Onyx 34L has a lower tantalum concentration resulting in less streak artefact on CT. Onyx is delivered through a microcatheter under fluoroscopic control.
There are several practical considerations when using Onyx™. Vials need to be shaken for at least 20 minutes and until they are ready to be drawn up for injection (Figure 2). A separate clean trolley and clean gloves are advised to prevent inadvertent polymerisation. The microcatheter should be DMSO compatible. The dead space of the microcatheter is filled with DMSO prior to injecting Onyx slowly (<0.3mL/min) under fluoroscopic guidance during injection.
Complex visceral aneurysms may be treated with Onyx using a balloon-assisted technique (Figure 3). A DMSO-compatible microcatheter is positioned with its tip in the centre of the aneurysm. Then a compliant balloon is placed across the neck of the aneurysm to isolate it from the parent vessel. The microcatheter is primed with DMSO to fill its dead space and Onyx is injected via the microcatheter until a sufficient volume (usually 0.2 ml) has been introduced, so Onyx reaches the end of the catheter. Onyx is then injected slowly with the occlusion balloon inflated.
Onyx accumulates around the tip of the microcatheter and forms a nidus that stays attached to the catheter. Occasional intermittent balloon deflation is performed to perfuse the end organ. The aneurysm is progressively filled until Onyx flows to the margins of the balloon and occludes the neck of the aneurysm flush with the arterial wall. Following angiographic confirmation of complete aneurysm exclusion, a ten-minute pause is taken to allow complete solidification of the polymer. The balloon is then reinflated and the microcatheter is removed by gentle traction.
Advantages of Onyx over an adhesive agent such as N-butyl-cyanoacrylate (NBCA) include no risk of the catheter becoming permanently adherent to the aneurysm wall. Embolisation with Onyx is less painful than NBCA as polymerisation is not exothermic and does not cause an inflammatory reaction. Onyx does not adhere to the arterial wall and therefore does not interfere with subsequent surgical repair.
On the other hand, widespread use of Onyx is prohibited by its high cost. In addition, it produces significant streak artefact on follow-up CT, often rendering them non-diagnostic for the purposes of aneurysm assessment. The authors have also experienced aneurysm reperfusion eight years after successful embolization with Onyx requiring re-intervention. Similar cases of Onyx resorption with recanalization of intracranial AVMs have also been reported.
Figures: Please click on the images to expand
Figure 1. Onyx preparations
Figure 2. Shaking Onyx prior to use
Figure 3. (A) Selective renal angiogram shows a 3cm fusiform aneurysm with a wide neck arising from main lower pole artery (B) Microcatheter within the aneurysm and a 3 x 40mm balloon inflated across the aneurysm neck excluding the aneurysm from parent artery (C) Onyx injected slowly into aneurysm via microcatheter (D) Completion angiogram shows complete aneurysm embolisation with no loss of renal parenchyma.
Joo Young Chun
St George's University Hospitals, London/GB
Joo Young Chun is a consultant interventional radiologist at St George's University Hospital in London with a special interest in arterial intervention. She is a member of many committes including the CIRSE Standards of Practice committee, BSIR Education and Research Committee, and EBIR Examination Council. She is an associate editor for CVIR Endovascular and a RCR FRCR 2B examiner.
St George's University Hospitals, London/GB
Robert Morgan is a professor of interventional radiology at St George’s University Hospital in London, as well as the Deputy Editor-in-Chief of CVIR Endovascular, and former President of CIRSE.
- Belli AM, Markose G, Morgan R. The role of interventional radiology in the management of abdominal visceral artery aneurysms. Cardiovasc Intervent Radiol 2012; 35: 234–43. 2.
- Chung R, Touska P, Morgan R, Belli AM. Endovascular management of true renal arterial aneurysms: Results from a single centre. Cardiovasc Intervent Radiol 2016; 39: 36–43
- Bratby MJ, Lehmann ED, Bottomley J, Kessel DO, Nicholson AA, McPherson SJ, Morgan RA, Belli AM. Endovascular Embolization of Visceral Artery Aneurysms with Ethylene-vinyl Alcohol (Onyx): A Case Series. Cardiovasc Intervent Radiol 2006; 29:1125–1128
- Andrew M Bauer,Mark D Bain, and Peter A Rasmussen. Onyx resorbtion with AVM recanalization after complete AVM obliteration. Interv Neuroradiol 2015;21: 351–356.
- Adamczyk P, Amar AP, Mack WJ, Larsen DW. Recurrence of “cured” dural arteriovenous fistulas after Onyx embolization. Neurosurg Focus 2012; 32: E12