Onyx Embolization of Tentorial Dural Arteriovenous Fistulas
Onyx Embolization of Tentorial Dural Arteriovenous Fistulas
We have demonstrated a high rate of complete obliteration and safety of Onyx embolization for tentorial DAVFs. Specifically, 89% of patients with a tentorial DAVF embolized with Onyx had total or near-total obliteration and no complications were exhibited during any of the endovascular procedures. Clinically, 89% of symptomatic patients experienced complete resolution of their symptoms, whereas those presenting with hemorrhage did not experience recurrent bleeds after a mean clinical follow-up time of 4.6 months.
Onyx is a mixture of ethylene vinyl alcohol dissolved in dimethylsulfoxide with tantalum powder added to make the mixture radiopaque. The dissolved polymer is delivered through a microcatheter, and once the polymer is in contact with an aqueous environment it starts to precipitate. Because its ability to disrupt blood flow is based on precipitation and not polymerization, the kinetics are more predictable than glues, such as N-butyl cyanoacrylate. Transarterial N-butyl cyanoacrylate embolization of DAVFs is highly operator dependent because the glue quickly polymerizes (unless a wedge position can be achieved), often leading to inadequate filling of the proximal draining vein. Complete filling of the proximal vein is a critical component for definitive endovascular cure of these lesions. Onyx represents a more controllable solution to treating DAVFs with direct cortical venous drainage from the arterial side. The unique features of Onyx make it ideally suited for the treatment of DAVFs with direct cortical venous drainage, and it has profoundly changed our practice for this specific type of DAVF, which until a few years ago was almost exclusively treated with open surgical exclusion at our institution. Because the Onyx permeates the actual fistula, it often refluxes into incoming additional small feeders, ensuring progressive slowing of incoming blood while the fistulous tract and the proximal portion of the draining vein are being obliterated. While the embolization progresses, it is important not to end the procedure as soon as the material is seen permeating the proximal draining vein. This embolizing material often coats the wall of the vessel before actually filling the entire lumen. Thus, angiographic opacification of the proximal vein with Onyx is not always synonymous with complete obliteration. In the final stages of the embolization, it is also critical to use a low frame rate and allow the angiogram to run well into the late venous phase to rule out small persistent and delayed filling of the fistula. One of the limitations of Onyx is the issue of reflux, because the material has a tendency to reflux alongside the microcatheter during injection. While the material is refluxing, care has to be taken to avoid migration of the material into dangerous anastomoses and/or retrograde filling of important branches (in the case of the posterior branch of the MMA, the petrous branch to the facial nerve). Microcatheter retrieval is usually not a major issue even in the setting of significant reflux because, in the external artery carotid system, a much higher traction can be safely applied than in the case of parenchymal vessels.
Other authors have observed similar rates of high angiographic obliteration when using Onyx for tentorial DAVFs. Unlike our own series, however, these previous studies reported relatively high rates of complications. These complications, reported in up to 24% of treatments, included venous rupture, migration of the Onyx embolus, trigeminocardiac reflex in 10% of patients, and tissue infarction due to Onyx reflux through anastomoses. Anatomical and technical considerations are key to avoiding perioperative complications. We found that the availability of a "sizeable" posterior branch of the MMA is critical to the success of Onyx embolization for tentorial DAVFs. The posterior branch of the MMA is a relatively straight vessel and is often enlarged when feeding a DAVF. These characteristics allow for distal catheterization adjacent to the point of the fistula, unlike other common feeders such as the OA, which is often excessively tortuous and makes distal catheterization difficult if not impossible. Distal catheterization almost in a wedge position allows for forward progression of the embolic material, limiting the reflux to a minimum. When embolizing from the posterior MMA branch, it is critical to avoid any reflux into the petrosal branch, which supplies the facial nerve.
Discussion
We have demonstrated a high rate of complete obliteration and safety of Onyx embolization for tentorial DAVFs. Specifically, 89% of patients with a tentorial DAVF embolized with Onyx had total or near-total obliteration and no complications were exhibited during any of the endovascular procedures. Clinically, 89% of symptomatic patients experienced complete resolution of their symptoms, whereas those presenting with hemorrhage did not experience recurrent bleeds after a mean clinical follow-up time of 4.6 months.
Onyx is a mixture of ethylene vinyl alcohol dissolved in dimethylsulfoxide with tantalum powder added to make the mixture radiopaque. The dissolved polymer is delivered through a microcatheter, and once the polymer is in contact with an aqueous environment it starts to precipitate. Because its ability to disrupt blood flow is based on precipitation and not polymerization, the kinetics are more predictable than glues, such as N-butyl cyanoacrylate. Transarterial N-butyl cyanoacrylate embolization of DAVFs is highly operator dependent because the glue quickly polymerizes (unless a wedge position can be achieved), often leading to inadequate filling of the proximal draining vein. Complete filling of the proximal vein is a critical component for definitive endovascular cure of these lesions. Onyx represents a more controllable solution to treating DAVFs with direct cortical venous drainage from the arterial side. The unique features of Onyx make it ideally suited for the treatment of DAVFs with direct cortical venous drainage, and it has profoundly changed our practice for this specific type of DAVF, which until a few years ago was almost exclusively treated with open surgical exclusion at our institution. Because the Onyx permeates the actual fistula, it often refluxes into incoming additional small feeders, ensuring progressive slowing of incoming blood while the fistulous tract and the proximal portion of the draining vein are being obliterated. While the embolization progresses, it is important not to end the procedure as soon as the material is seen permeating the proximal draining vein. This embolizing material often coats the wall of the vessel before actually filling the entire lumen. Thus, angiographic opacification of the proximal vein with Onyx is not always synonymous with complete obliteration. In the final stages of the embolization, it is also critical to use a low frame rate and allow the angiogram to run well into the late venous phase to rule out small persistent and delayed filling of the fistula. One of the limitations of Onyx is the issue of reflux, because the material has a tendency to reflux alongside the microcatheter during injection. While the material is refluxing, care has to be taken to avoid migration of the material into dangerous anastomoses and/or retrograde filling of important branches (in the case of the posterior branch of the MMA, the petrous branch to the facial nerve). Microcatheter retrieval is usually not a major issue even in the setting of significant reflux because, in the external artery carotid system, a much higher traction can be safely applied than in the case of parenchymal vessels.
Other authors have observed similar rates of high angiographic obliteration when using Onyx for tentorial DAVFs. Unlike our own series, however, these previous studies reported relatively high rates of complications. These complications, reported in up to 24% of treatments, included venous rupture, migration of the Onyx embolus, trigeminocardiac reflex in 10% of patients, and tissue infarction due to Onyx reflux through anastomoses. Anatomical and technical considerations are key to avoiding perioperative complications. We found that the availability of a "sizeable" posterior branch of the MMA is critical to the success of Onyx embolization for tentorial DAVFs. The posterior branch of the MMA is a relatively straight vessel and is often enlarged when feeding a DAVF. These characteristics allow for distal catheterization adjacent to the point of the fistula, unlike other common feeders such as the OA, which is often excessively tortuous and makes distal catheterization difficult if not impossible. Distal catheterization almost in a wedge position allows for forward progression of the embolic material, limiting the reflux to a minimum. When embolizing from the posterior MMA branch, it is critical to avoid any reflux into the petrosal branch, which supplies the facial nerve.