Basics and principles in the application of Onyx LD liquid embolic system in the endovascular treatment of cerebral arteriovenous malformations

Onyx is a new liquid embolic system (Micro Therapeutics, Inc., Irvine, CA) consisting of ethylene-vinyl alcohol copolymer (EVOH), formed of 48 mol/L ethylene and 52 mol/L vinyl alcohol, dissolved in dimethyl-sulfoxide (DMSO) and mixed with micronized tantalum powder (35% weight per volume) for radiopaque visualization. In its low density form it is predominantly used worldwide in the treatment of cerebral(1-6) or spinal(7.8) arteriovenous malformations (AVMs), other more rare indications are hypervascularized tumors(9), peripheral AVMs or arteriovenous fistulas (AVFs)(10), and there is also an extensive use in experimental work (11-12). Onyx LD means low density of EVOH in the range of 6 to 8 % (Onyx 18 to 34) compared to high density Onyx 500(+) (containing 20 % of EVOH) used for aneurysm occlusions. The basics of Onyx LD liquid system and the main principles of its application in endovascular AVM therapy are described and discussed in this chapter.