Curative Embolization with Onyx of Dural Arteriovenous Fistulas with Cortical Venous Drainage

Discussion

Our initial experience in a small patient group by using Onyx for DAVFs with cortical venous drainage is hopeful and confirms the good results reported by others.^14–18 Since we adopted Onyx as treatment of choice for these aggressive and rare lesions, all patients could be cured in a single session and mostly with only 1 Onyx injection of less than a half-hour duration. The technique we used to inject Onyx in DAVFs is comparable with the technique for the treatment of brain arteriovenous malformations¹⁹: Once a distal position of the tip of the microcatheter in a dural feeder close to the fistula is reached, reflux is slowly built up with a 1- to 3-minute pause between injection attempts until the feeding artery is plugged and Onyx starts to advance into the fistula and the draining veins. Sometimes 5–15 attempts are needed before Onyx advances; thus, patience is required. When in a long feeding vessel (mostly the anterior division of the middle meningeal artery), a distal position is obtained, reflux of 5 cm or even more can be accepted, and many injection attempts are possible. Even after injections of almost half an hour with a long segment of reflux, the Rebar microcatheter could be retrieved without difficulty. Thus, the length of reflux in these dural arteries is not directly related to the possibility of removal of the microcatheter. Onyx does not react with or stick to the vessel wall; it merely fills the vessel lumen.²⁰ Therefore, it is important to completely fill all vessels involved in the fistulous complex; deposition of Onyx in the proximal draining vein only may not be sufficient to completely occlude the fistula or may give rise to recurrence at follow-up.

We suspend the injection for a short period of time when Onyx starts to fill the veins. With repeated injection, additional Onyx often initially is deposited more proximally, including retrograde filling of other dural feeders, before further distal advancement in the veins. This technique can be repeated several times, thereby slowly achieving complete occlusion of the fistula, all dural feeders, and the proximal draining veins with complete luminal filling. In selected cases, a microballoon proximal to the tip of the Onyx microcatheter can help in this injection process by preventing reflux and stimulating advancement of the Onyx.¹⁸ In our experience, confirmed by others,^15,17 the middle meningeal artery is the most suitable for Onyx injection; it is often involved in dural fistulas and can be readily catheterized to a distal position, and long segments of reflux can be accepted because microcatheter removal proved to be easy in such cases. Whenever this artery contributes to the fistula, we try to use it for embolization.

Other vessels such as the occipital artery are mostly more tortuous and less easy to catheterize. When the tentorial artery is involved and has to be used as access for embolization, we probably still prefer injection of acrylic glue under protection of a microballoon across the origin in the internal carotid artery.²¹ Although we had no complications of treatment, postprocedural pain was experienced by most patients, and adequate pain medication was needed in some patients. Pain is probably related to ischemia of the dura as a result of occlusion of dural arteries. Pain usually gradually decreased in the following days to weeks, and at the time of follow-up angiography after 6–12 weeks, no patients used analgesics.

Another matter of concern is the radiation dose. Often many angiographic runs are necessary to document the dural fistula. In addition, prolonged Onyx injection during fluoroscopy adds to this dose. For dose reduction, we avoid simultaneous biplane fluoroscopy, and we approximate the flat panels as near as possible to the patient's head.

As with other embolic agents, complications with Onyx may occur. Ischemic damage to the trigeminal and facial nerve may be associated with too proximal reflux of Onyx in the middle meningeal artery beyond the foramen spinosum when occlusion of cavernous and petrosal branches may occur. Reflexive bradycardia may be associated with the treatment of tentorial DAVFs. When anastomoses of external carotid artery branches to the vertebrobasilar system remain unrecognized, migration of Onyx may cause posterior circulation infarctions.^22–24 However, in our opinion, with proper technique and sufficient anatomic knowledge, these complications can mostly be avoided.