Dr Geert Maleux, University Hospitals Leuven, Belgium, presented a breakfast symposium at the recent Global Embolization Symposium and Technologies (GEST) meeting, discussing the use of the embolic agent, Onyx (ev3), for the treatment of peripheral high-flow arteriovenous malformations (AVM).
Maleux explained that there are a wide variety of high-flow AVM classification systems and referred to a study by Mulliken and Glovicki (1982) who reported on two different entities, haemangioma and vascular malformation, which typically include arterial, capillary, venous and lymphatic.
High-flow AVM, according to Maleux, have a high speed of flow through the lesion and a high rate of shunting between arteries and veins. Diagnosis is usually performed by physical examination, MRI and/or catheter angiography, and treatment can be surgical (although questionable by Maleux) or by transcatheter embolisation.
What is the ideal agent for high-flow AVM?
Maleux suggested that embolic agents for the treatment of AVMs should accommodate the following points:
• Penetrate and occlude the abnormal vascular communications
• Provides permanent occlusion
• Non-toxic
• Non-allergenic
• Non-clumping
• Controlled injection through a microcatheter
• Radiopaque
• Inexpensive
Maleux then said that other embolic agents such as coils, plugs or detachable balloons have no distal penetration and polyvinyl alcohol (PVA) has a risk of pulmonary embolism, and late recanalisation.
Liquids, such as Trufill (Cordis), Histoacryl (B. Braun), and Glubran (GEM), polymerises in contact with blood, produces an exothermic reaction and normally need quick microcatheter removal. Other liquids, eg. alcohol (ethanol), are sclerosing agents which have direct toxic effect on the endothelium.
Following, Maleux explained that Onyx consists of:
• Ethylene vinyl alcohol co-polymer
• Dimethyl sulfoxide solvent (DMSO)
• Tantalum powder
In describing the working mechanism of Onyx, he said that in situ precipitation and solidification of the polymer is time-dependent, affected by the amount of ethylene, and concentration of copolymer dissolved in DMSO - which determines the viscosity of Onyx. The agent also enables the formation of an elastic soft, spongy cast without adhesion to the vascular wall, said Maleux (see Figure 1).
Some of the advantages of using Onyx include no risk for catheter gluing, slow, intermittent injection, transembolisation angiography, ability to conform to the shape of tortuous arteries, and preservation of the option for subsequent surgical resection. However, there are some disadvantages associated with the agent, and Maleux explained them to be:
• Non-target embolisation is not excluded
• Catheterisation and embolisation of parasitic feeders is not always possible
• Pain during injection (sedation or general anaesthesia)
• High cost
Technique
The technique used for treating AVM with Onyx involves a mixer (shaking for 20min), microcatheter (eg. Rebar, Silver Speed, ev3) which is DMSO-compatible and allows for slow injection (see Figure 2).
The results of a brain AVM in which Onyx was used, were described by Mounayer et al., (2007). It was reported higher rates of anatomic cure compared with other embolic agents. The procedure-related permanent neurologic deficits was 8.5%, explained Maleux.
Other, extracranial indications for Onyx include type II-endoleak, embolisation of pseudoaneurysm of the deep femoral artery and abdominal and thoracic aneurysms.
In summarising, Maleux stated that Onyx for high-flow AVM is safe and efficacious due to controlled injection, no catheter gluing and results in a low incidence of non-target embolisation. Specific materials are required eg. microcatheter and shaker, and there is still much learning to be done.
Finally, he said that Onyx has become his preferred embolic agent for the treatment of peripheral high-flow AVM.
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