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Neurology India, Vol. 58, No. 1, January-February, 2010, pp. 1-2 Editorial Evolution of endovascular treatment of intracranial dural arteriovenous fistulas Bulang Gao Institute of Diagnostic and Interventional Radiology, Shanghai Sixth People's Hospital, Shanghai Jiaotong University, Shanghai, China and Cerebrovascular and Endovascular Division, Department of Neurosurgery, Tufts University Medical Center, Boston, USA Correspondence Address: Dr. Bulang Gao, Cerebrovascular and Endovascular Division, Department of Neurosurgery, Tufts University Medical Center, 750 Washington Street, Boston - 02111, USA, browngao@yahoo.com.cn Date of Acceptance: 05-Jan-2010 Code Number: ni10001 DOI: 10.4103/0028-3886.60385 Intracranial dural arteriovenous fistulas (DAVFs) are abnormal connections between dural arteries and venous sinuses or leptomeningeal veins and account for 10-15% of all intracranial arteriovenous shunts. [1] The origin of these malformations is not entirely understood. Most often DAVFs have been found in association with venous thrombosis, intracranial surgery, tumor, puerperium and trauma. [2] DAVFs may be asymptomatic or may present with a wide range of symptoms including tinnitus, intracranial hemorrhage and severe neurologic deficits. The venous drainage pattern of the DAVFs determines the risk of hemorrhage. Cortical veins exposed to arterial pressure may develop venous aneurysms, ectasias and stenoses, thus increasing the risk of intracranial hemorrhage. The treatment goal in these patients should be a complete cure. Intracranial DAVFs can be treated through stereotactic radiosurgery, surgical intervention, transarterial or transvenous embolization, or a combination of these strategies. Surgery can be technically demanding, it places adjacent brain parenchyma in danger, and it carries risks common to all craniotomies. Radiosurgery with Gamma Knife has varying success rates (44-87%), [3] although these procedures do not offer an immediate solution. The results may be improved in conjunction with various endovascular approaches. The transvenous approach consists of retrograde catheterization and sacrifice of the involved venous structure (usually a dural sinus). This approach has high rates of cure and total obliteration of the fistula, however, it may be associated with severe complications such as vessel rupture, venous infarct and intracranial hemorrhage. [4] The transarterial approach is to super-selectively catheterize the dural arteries supplying the DAVF for delivery of embolic agents. Highly flexible, hydrophilic, and distal navigation catheters facilitate complete occlusion of small dural arteriovenous shunts. This technique may be facilitated by a limited number of feeding vessels and a wedged position which allows injection of embolic agents in a relatively controlled manner. Detachable coils, silk sutures, polyvinyl alcohol (PVA), and n-butyl-2-cyanoacrylate (NBCA) have been used as embolic agents for endovascular management of DAVFs. The number of reports of DAVF patients treated with Onyx embolization is increasingly on the rise in the recent literature, and the study by Saraf et al., [5] in this issue, contains the largest cohort of such patients treated this way with the highest cure rate (92%) and the lowest non-mortality complication rate (5%). Although PVA particles are easy to handle, they often result in proximal occlusion. The shunting flow can be reduced with PVA, however, permanent cure is difficult to achieve with this method alone. For this reason, PVA embolization is usually not recommended as sole therapy for aggressive lesions. NBCA has been used to treat DAVFs with variable success rates. Total and permanent fistula occlusion can be achieved with NBCA, particularly when the embolic material reaches the fistulous connection. The major disadvantage of this technique is the unpredictable nature of NBCA polymerization, often resulting in inadequate penetration into the fistula. Moreover, NBCA is an adhesive agent, risking permanent retention of the microcatheter. Onyx is a new nonadhesive liquid agent containing a mixture of ethylene-vinyl alcohol copolymer and dimethyl sulfoxide (DMSO). While DMSO diffuses under aqueous conditions, the ethylene-vinyl alcohol copolymer precipitates and mechanically occludes the feeding vessels. Compared with NBCA, Onyx is nonadhesive. The advantages of a nonadhesive liquid are a decreased risk of gluing the catheter and the ability to inject a larger volume of agent per administration. Moreover, Onyx injection is easier to control than NBCA injection, injection in a single feeder allows obtaining arterio-arterial reflux and avoids embolization of other feeders, and access through the meningeal artery is more efficient even if the size is very small. Onyx is now used as an alternative to cyanoacrylates in many brain arteriovenous malformations [6] and in many therapeutic reports of both intracranial and extracranial DAVFs, Onyx has also been applied with good results. [1],[2],[3],[5],[6],[7],[8],[9],[10] Prior to the introduction of Onyx, the goal of endovascular embolization varied between cases and included attempted curative occlusion of the fistula, reduction of the shunt volume to facilitate surgery and in some cases palliation of symptoms. Therapeutic strategies evolved following the introduction of Onyx, and the current purpose of endovascular management with Onyx is curative occlusion of the fistula. [9] Despite the advantages of Onyx, adverse events, such as catheter rupture or entrapment, angiotoxicity, and Onyx reflux into normal branches causing ischemic events, have been reported with Onyx injection. [1],[2],[3],[5],[6],[7],[8] Potential reasons for catheter rupture or entrapment are the pressure required to move the Onyx plug forward, the length or density of reflux, the tortuosity of feeding vessels, and the injection time. Angiotoxicity with vasospasm or angionecrosis is probably caused by the use of DMSO whose angiotoxicity is dependent on the volume injected and time in contact with the endothelium. Although such events are uncommon, extra care should be taken to prevent adverse events from happening for the sake of the health of the patients. Moreover, the effect of Onyx embolization for intracranial DAVFs needs a long-term test both angiographically and clinically even though the short-term results are promising. The introduction of Onyx has markedly improved the endovascular ambition and capability to treat DAVFs because of advances in microcatheter and embolic material technology, and these advances have made the endovascular approach the treatment of choice for the majority of DAVFs requiring intervention and have also made low complication rates possible. References
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