Liquid Embolic Agents for Endovascular Embolization: Evaluation of an Established (Onyx) and a Novel (PHIL) Embolic Agent in an In Vitro AVM Model

BACKGROUND AND PURPOSE:Embolization plays a key role in the treatment of arteriovenous malformations. The aim of this study was to evaluate an established (Onyx) and a novel (precipitating hydrophobic injectable liquid PHIL]) liquid embolic agent in an in vitro AVM model.MATERIALS AND METHODS:An AVM model was integrated into a circuit system. The artificial nidus (subdivided into 28 honeycomb-like sections) was embolized with Onyx 18 (group Onyx; n = 8) or PHIL 25 (group PHIL; n = 8) with different pause times between the injections (30 and 60 seconds, n = 4 per study group) by using a 1.3F microcatheter. Procedure times, number of injections, embolization success (defined as the number of filled sections of the artificial nidus), volume of embolic agent, and frequency and extent of reflux and draining vein embolization were assessed.RESULTS:Embolization success was comparable between Onyx and PHIL. Shorter pause times resulted in a significantly higher embolization success for PHIL (median embolization score, 28 versus 18; P = .011). Compared with Onyx, lower volumes of PHIL were required for the same extent of embolization (median volume per section of the artificial nidus, 15.5 versus 3.6 μL; P < .001).CONCLUSIONS:While the embolization success was comparable for Onyx and PHIL, pause time had a considerable effect on the embolization success in an in vitro AVM model. Compared with Onyx, lower volumes of PHIL were required for the same extent of embolization.

Arteriovenous malformations are complex vascular structures composed of feeding arteries, an intervening network of small pathologic blood vessels (the so-called nidus), and draining veins. The lack of an intervening capillary bed allows high-flow arteriovenous shunting of blood. While AVMs can occur throughout the entire body, cerebral AVMs are of particular relevance due to their ability to cause impairing neurologic symptoms and their considerable risk of hemorrhage.¹Alone or in combination with microneurosurgery and stereotactic radiation therapy, embolization plays an important role in the management of cerebral AVMs.² The aim of AVM embolization is complete filling of the nidus, while unwanted reflux into the feeding arteries should be minimized and premature embolization of the draining veins should be avoided.³A wide variety of embolic agents has been and is currently used for embolization of AVMs. At present, the liquid embolic agents (LEAs) ethylene-vinyl alcohol copolymer (EVOH) and n-butyl cyanoacrylate are used most frequently.⁴ Although the embolization results have improved since the introduction of EVOH-based LEAs with rates of complete obliteration ranging from 16% to 100%, the success rate of AVM embolization, especially for complex AVMs, is not yet satisfying.^2,3 Currently, new LEAs are being introduced to improve embolization features, such as embolization efficacy, intraprocedural handling, and control. Furthermore, their use should improve fluoroscopic visibility and reduce artifacts in postinterventional imaging.The aim of this study was to evaluate an established EVOH-based embolic agent and a novel copolymer-based embolic agent in an in vitro AVM model.