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

Discussion

In our small series of patients with dAVFs, we achieved complete occlusion or reduction of flow to a minimal residual fistula in 88.9% of the cases after 1 embolization attempt, with complete improvement of the initial symptoms during follow-up. One patient with a residual fistula was treated again, which led to occlusion of the parent sinus followed by clinical cure. There were no immediate or delayed permanent postinterventional complications.

During the past few decades, endovascular embolization with liquid embolic material, particles, or coils has become the first-line treatment for a wide range of dAVFs. Several transarterial and transvenous endovascular approaches have been advocated. Recent technical improvements include the introduction of dimethyl-sulfoxide–compatible double-lumen balloon microcatheters for transarterial embolization and dedicated especially designed venous balloons for transvenous sinus protection. Combining the advantages of transarterial balloon-assisted embolization with transvenous balloon protection seems to be a promising treatment strategy. Formerly, use of the technique had only been reported in small case series as part of different endovascular treatment approaches for dAVFs.^2,8,13

The introduction of dimethyl-sulfoxide–compatible double-lumen balloon microcatheters for transarterial embolization of dAVFs with Onyx has shown encouraging results in preliminary studies, with high occlusion and low complication rates.^{1⇓⇓⇓⇓⇓⇓⇓–9,16} In the largest study available, Kim et al⁵ compared the results of transarterial Onyx embolization for dAVFs using a double-lumen balloon with those obtained by using a nonballoon microcatheter. The use of a double-lumen balloon microcatheter led to an increased immediate complete occlusion rate, decreased procedure time, decreased Onyx injection time, and a decrease in the number of feeders requiring embolization compared with the group treated with a nonballoon microcatheter. The main advantages of double-lumen balloon-assisted embolization are immediate control of the antegrade flow of the embolic material without the need for proximal plug formation, more effective distal penetration into the fistula and possibly into the distal portion of other arterial feeders, and the prevention of reflux into adjacent arteries.⁵ The larger profile and greater stiffness of the balloon microcatheter compared with dedicated low-profile embolization microcatheters mean that a satisfactory distal injection position may not be reachable due to small vessel caliber or tortuosity.³ In our series, delivery of the balloon microcatheter was possible through the middle meningeal artery in all cases; this artery usually has a rather straight course, facilitating microcatheterization. The potential risk of vessel rupture as a result of overinflation of the balloon² can be avoided by carefully inflating the balloon under fluoroscopic control.

Transvenous balloon protection during transarterial embolization was first proposed by Shi et al⁸ with a small compliant balloon originally designed for aneurysm remodeling. The introduction of a large dedicated dimethyl-sulfoxide–resistant single-lumen compliant balloon catheter for transvenous sinus occlusion (8 × 80 mm, Copernic RC) has facilitated this adjunctive technique and paved the way for its wider use. The advantages of transvenous balloon protection during simultaneous transarterial embolization include the prevention of inadvertent occlusion of the lumen of a functioning sinus required for cerebral venous drainage and propagation of embolic material into adjacent cortical or deep cerebral veins. Ertl et al¹³ recently conducted a retrospective comparison of sinus-preserving and sinus-occluding endovascular treatment techniques for low- and intermediate-grade dAVFs involving the transverse and sigmoid sinuses (Cognard type I–IIb). A higher rate of permanent fistula occlusion was achievable with sinus-occluding techniques than with the sinus-preserving technique (93% versus 71%), but this came at the cost of a higher complication rate (33% versus 0%). These results are in accordance with our findings using a combined transarterial and transvenous approach for sinus-preserving dAVF embolization, showing no permanent complications and a high rate of remission of clinical symptoms with a single treatment session. Two-thirds of our patient population presented with a low-grade dAVF with a known benign natural history and thus relative and no vital treatment indication, despite the disturbing tinnitus. Every treatment attempt should aim for the lowest risk of complications and the most favorable benefit-risk ratio.

Despite a small residual shunt in 5 patients, after the embolization session, all patients experienced remission of clinical symptoms with spontaneous complete occlusion in 4 patients during follow-up and subsequently complete clinical cure (1 patient refused the follow-up angiography due to clinical cure). Furthermore, transvenous balloon placement in the sinus was helpful to understand the vascular anatomy of the fistula network and its venous drainage during embolization. Parallel venous channels as recipients for the arterial shunt into the transverse/sigmoid sinus and multiple arteriovenous connections within the dural wall and not the sinus itself can be observed.^17⇓–19 These venous recipient structures may be obscured and not distinctly identified during angiography and transarterial embolization. The use of transvenous balloon protection with inflation of the balloon within the main sinus lumen, covering the entire length of the diseased sinus, facilitates the identification and occlusion of these abnormal arteriovenous connections within the sinus wall and separates venous channels by enabling increased penetration of embolic material by retrograde reflux into other dural feeders of the fistula network. At the same time, the technique allows sinus patency control and provides continuous injection of liquid embolic material, minimizing the risk of leakage into the sinus.^8,10⇓–12

Although no permanent clinical complications occurred in our series, inadvertent propagation of Onyx into the proximal vein of Labbé was noted despite balloon inflation inside the main sinus lumen in 1 patient (No. 6), most probably the result of retrograde leakage of liquid embolic material along a parallel channel. This finding emphasizes the necessity of monitoring and adjusting balloon pressure appropriately and carefully observing the Onyx penetration along the dural sinus. An inflation time of 2–5 minutes has been used with temporary deflation of the balloon during cessation of Onyx injection to avoid venous infarction due to prolonged transvenous balloon occlusion, especially in the dominant sinus or in those cases involving normal cortical veins.¹¹

The limitations of our study include its retrospective nature, the small sample size, and, for some patients, the short follow-up period. However, the results were obtained in consecutive patients with a defined pathology who were treated with a standardized endovascular approach.