Cerebral dural arteriovenous fistulas (dAVFs) are characterized by pathologic direct shunts between dural arteries and veins or a venous sinus, with the fistula point or zone located at the dural level. Most often they are found at the wall of the transverse sinus (50%), the cavernous sinus (16%), the superior sagittal sinus (8%), or at the tentorium cerebelli (12%).¹ dAVFs are an acquired disease, probably based on (transient) venous thrombosis inducing venous hypertension and subsequently progressive arterialization of the venous vessel wall.

Microvascular connections within the dura might be intrinsic² and become activated and later hypertrophied, or might be a result of neovascularization³ promoted by angiogenic growth factors. Most practically, dAVFs are classified according to Borden et al⁴ and Cognard et al,⁵ with higher grades indicating an increased risk for cerebral hemorrhage. Due to technical innovations like the development of compliant, inflatable occlusion balloons and liquid embolic agents, endovascular embolization has been established as the first-line treatment for dAVFs. Basically, sinus-preserving and sinus-occluding embolization techniques can be distinguished.

The occlusion of a dural sinus, however, carries a risk of venous infarction or hemorrhage. The sinus-preserving technique by transarterial embolization with liquid embolics requires superselective catheterization of arterial feeders to deliver the embolic agent. Onyx (Covidien, Irvine, California) has been widely used as a liquid embolic agent for transarterial embolization,^6-8 allowing considerable penetration and casting of the fistula site, but also harboring the risk of accidental embolization of the distal venous system, which may result in the exacerbation of venous hypertension, venous infarction, and/or hemorrhage. Sinus-occluding techniques are still effective treatment options, with a high rate of definite fistula occlusion, but at the cost of a relevant, associated complication rate.⁹

Thus, nowadays sinus-preserving treatments are favored as primary therapeutic options, especially in low-grade fistulas, because the natural venous drainage pattern can be maintained. If complete fistula occlusion may not be possible or cannot be reached, downgrading the dAVF can also be a treatment goal. Due to novel technical developments, the neuroendovascular armamentarium is growing and dAVF management is further evolving, as highlighted in this edition of the AJNR News Digest.

Transarterial dAVF embolization using Onyx as the sole endovascular embolic agent is an effective treatment strategy that has a low complication rate and allows a high rate of durable long-term cure.¹⁰

The combination of transarterial liquid embolization and transvenous balloon-assisted protection of the venous sinus can prevent nontarget venous embolization and allows for retrograde embolization of arterial feeders by migration of the embolic agent along the balloon. This sinus-preserving technique can be considered safe and offers high rates of complete occlusion and symptom remission.¹¹

Using double-lumen balloon microcatheters for transarterial embolization and concomitant transvenous balloon protection of the venous sinus can also be considered a safe and highly curative technique.¹² Compared with nonballoon microcatheters for transarterial embolization, controlling the antegrade flow of the embolic agent without the need for proximal plug formation and preventing reflux into adjacent arteries are advantages of this approach.

The recent introduction of Precipitating Hydrophobic Injectable Liquid (PHIL; MicroVention, Tustin, California) as a new, nonadhesive liquid embolic agent has provided further impact on transarterial embolization. Using PHIL seems to allow a safe and effective endovascular dAVF treatment with the added advantages of easier preparation and more homogeneous cast visualization in comparison with Onyx.¹³

Furthermore, the understanding of dAVF angioarchitecture is evolving. A new conceptual model of lateral sinus dAVFs reduces the arteriovenous communications to 1 or several discrete fistulous point(s) between arteries in the wall of the dural sinus and the sinus lumen itself.¹⁴ An enlarged mural artery (common arterial collector) receives collective arterial inflow through numerous arterial anastomoses and serves as a final common conduit supplying a simple fistulous site. This concept allows a highly targeted dAVF treatment by occluding these artery-to-sinus communications, while the venous sinus proper can be preserved and inadvertent embolization of vessels not directly involved in the pathologic arteriovenous shunt can be reduced.

References

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4. Borden JA, Wu JK, Shucart WA. A proposed classification for spinal and cranial dural arteriovenous fistulous malformations and implications for treatment. J Neurosurg 1995;82:166–79, 10.3171/jns.1995.82.2.0166.
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9. Ertl L, Brückmann H, Kunz M, et al. Endovascular therapy of low- and intermediate-grade intracranial lateral dural arteriovenous fistulas: a detailed analysis of primary success rates, complication rates, and long-term follow-up of different technical approaches. J Neurosurg 2017;126:360–67, 10.3171/2016.2.JNS152081.
10. Chandra RV, Leslie-Mazwi TM, Mehta BP, et al. Transarterial onyx embolization of cranial dural arteriovenous fistulas: long-term follow-up. AJNR Am J Neuroradiol 2014;35:1793–97, 10.3174/ajnr.A3938.
11. Vollherbst DF, Ulfert C, Neuberger U, et al. Endovascular treatment of dural arteriovenous fistulas using transarterial liquid embolization in combination with transvenous balloon-assisted protection of the venous sinus. AJNR Am J Neuroradiol 2018;39:1296–1302, 10.3174/ajnr.A5651.
12. Piechowiak E, Zibold F, Dobrocky T, et al. Endovascular treatment of dural arteriovenous fistulas of the transverse and sigmoid sinuses using transarterial balloon-assisted embolization combined with transvenous balloon protection of the venous sinus. AJNR Am J Neuroradiol 2017;38:1984–89, 10.3174/ajnr.A5333.
13. Lamin S, Chew HS, Chavda S, et al. Embolization of intracranial dural arteriovenous fistulas using phil liquid embolic agent in 26 patients: a multicenter study. AJNR Am J Neuroradiol 2017;38:127–31, 10.3174/ajnr.A5037.
14. Shapiro M, Raz E, Litao M, et al. Toward a better understanding of dural arteriovenous fistula angioarchitecture: superselective transvenous embolization of a sigmoid common arterial collector. AJNR Am J Neuroradiol 2018;39:1682–88, 10.3174/ajnr.A5740.

Image: Vollherbst DF, Ulfert C, Neuberger U, et al. Endovascular treatment of dural arteriovenous fistulas using transarterial liquid embolization in combination with transvenous balloon-assisted protection of the venous sinus. AJNR Am J Neuroradiol 2018;39:1296–1302, 10.3174/ajnr.A5651.