**3.1 Embolization procedure**

Operator needs to know the goal of the endovascular treatment whether it is aiming a complete obliteration, presurgical grade reduction, size reduction before radiosurgery, or a targeted treatment to obliterate weak angioarchitectural points like flow-related aneurysms or intranidal aneurysm causing recurrent hemorrhage. Accordingly, with the specific aims, a game plan can be organized.

In most of the institutions, AVM embolization is performed under general anesthesia. Although some centers advocate conscious sedation over general anesthesia, we do not find it practical to perform embolization in awake patients considering potentially lengthy procedures and absolute need for immobilization during embolysate injection. Triaxial systems with intermediate distal access catheters provide the advantage of much needed stability and momentum in distal and tortuous arterial feeders. A distal access catheter can be navigated to the level of the supraclinoid internal carotid artery, basilar artery, and even in the middle cerebral artery M1 or posterior cerebral artery P1 segments to have a better support.

If the aim is cure or significant size reduction, the ideal position of the microcatheter will be as distal as possible and close to the nidus of the AVM. One must be very careful during microcatheter navigation within the arterial feeders that are prone to dissection or perforation. The safest navigation technique is pushing the

leading microcatheter with a microwire inside and without microwire coming off. Microwire can lead the microcatheter if there is a kink or tortuosity preventing the microcatheter to move forward alone. As soon as the kink or tortuosity is overcome, microwire is withdrawn inside. Navigation technique is different for flowdependent microcatheters like Magic microcatheter (Balt, Montmorency, France). These microcatheters can be pushed with injection of saline and contrast mixtures and gentle pushing. One must pay attention to avoid kinking of these microcatheters because of poor visibility of the microcatheter shaft that tends to fold on itself when there is too much forward momentum. Gentle superselective microcatheter injections demonstrate the component supplied by the pedicle, venous drainage, and speed of shunting. If there is normal parenchymal blush from the same pedicle, another pedicle is chosen to prevent nontargeted embolization. En passage feeders are challenging because it can be difficult to choose them selectively, and distance to the normal main branch is usually very short for a safe injection. Microcatheter is flushed with saline after contrast injection and before introducing the D5 for NBCA or DMSO for ETOH. The working angle with the longest and straightest view of the microcatheter avoiding overlapping of the nidus and microcatheter must be chosen for the superselective angiogram and liquid embolic injection.

Ideal liquid embolic injection aims to penetrate into the nidus, completely obliterate the nidus, and reach to the very proximal portion of the venous outflow (**Figure 5**). This can be challenging in AVMs with multiple feeders and single draining vein. If the venous outflow is occluded with remaining arterial feeders and a

#### **Figure 5.**

*(A–C) A previously ruptured cerebellar AVM in a 57-year-old-male with prior history of surgery for hematoma evacuation and partial resection of the AVM. (D and E) Complete obliteration of the AVM after embolization.*

*Endovascular Treatment of Cerebral Arteriovenous Malformations DOI: http://dx.doi.org/10.5772/intechopen.89185*

#### **Figure 6.**

*(A and B) An unruptured posterior fossa AVM. Final angiogram (C and D) after balloon microcatheterassisted embolization shows the onyx cast almost entirely matching with the AVM. (E and F) A tiny residual filling (arrow) without obvious early venous filling. Patient had surgery following embolization for complete resection of the AVM.*

large residual nidal component, a normal pressure breakthrough may occur leading to intracranial hemorrhage. Early venous stagnation with a residual persistent AVM can be an ominous sign and may require complete endovascular obliteration of the AVM if possible or immediate surgical resection (**Figure 6**).

Depending on the angioarchitectural characteristics and preferences and experience of the operator, EVOH or NBCA can be chosen. Although ETOH is used more frequently with the advantages of longer injection times or possibility of halting injections with intermittent angiographic control, NBCA is still preferred by some institutions [39]. Loh and Duckwiler [40] did not find significant differences between two agents in their capacity for at least 50% volume reduction, complication rates, and intraoperative blood loss. NBCA works through polymerization and requires meticulous preparation in order to prevent contamination with blood or saline that may cause premature polymerization. NBCA is prepared in a separate table or in an isolated part of the main table [40]. Operators change their gloves before preparation to prevent contamination and contact of blood with embolic agents. Microcatheter is flushed with D5 before NBCA injection. NBCA mixture can be tailored depending on the arteriovenous shunting. Most common mixture ratios of NBCA to Ethiodol are 1:3 or 1:2 (NBCA:Ethiodol). Denser mixtures can be used if there is a fistulous component with fast flow into the veins. More diluted mixtures can penetrate better into the nidus with the drawback of higher chance of reflux. Another technique to improve the NBCA penetration into the lesion is flushing the guiding catheter continuously with D5 dextrose solution while injecting the glue [41]. Penetration of the NCBA can be

stopped by stopping the D5 perfusion. NBCA is an adhesive agent and microcatheter must be removed briskly as soon as the reflux begins. In both NBCA and ETOH injections, microcatheter is removed while applying negative pressure by gentle aspiration.

ETOH (Onyx, Medtronic, Irvine, CA, USA or Squid, Emboflu, Gland, Switzerland) is a nonadhesive liquid embolic agent, which does not polymerize but precipitates when dissolved with dimethyl sulfoxide (DMSO). ETOH laminates along the venous wall without immediate occlusion of the vessel. Most frequently used ETOH-based liquid embolic agent is Onyx (Medtronic, Irvine, CA, USA). Dead space of the microcatheter is filled with the exact amount of DMSO before ETOH injection. Before injection, we usually mark the screen with a pen showing the landmarks including the most proximal tolerable reflux point on the microcatheter, boundaries of the AVM, and beginning of the venous drainage. Under blank roadmap, ETOH is injected slowly and reflux is watched. In the most popular "plug and push technique," reflux forms a plug of ETOH at the tip of the microcatheter. Some institutions prefer the denser version of ETOH like Onyx 34 (Medtronic, Irvine, CA, USA) to form a plug. After the precipitation of ETOH forming a plug, antegrade penetration into the nidus with new injections is expected. Whenever there is further reflux, penetration into another arterial branch, or early venous penetration, injection is stopped for approximately 90 s. Halting injection for more than 2 min may cause clogging of the microcatheter. If there is no ETOH coming off the microcatheter tip or appearing under blank roadmap 60–90 s after starting injection, injection must be stopped and microcatheter is removed. Clogging of the microcatheter can result in rupture of the microcatheter shaft and extravasation of ETOH [42]. Intermittent angiograms can be done to control the obliteration of the AVM and the status of venous drainage while halting ETOH injections. After a satisfying obliteration is achieved, microcatheter is removed from the system. In ETOH cases, microcatheter is removed by applying constant gentle tension on the microcatheter. If there is a stubborn microcatheter stuck in the ETOH cast, patience with repetitive pulling with constant tension will remove the microcatheter in most of the cases.

Advances in microcatheter technology, development of detachable tip microcatheters, ETOH compatible dual lumen microballoon catheters, and evolution of liquid embolic agents have changed the paradigms in the endovascular treatment.

#### **3.2 New trends in embolization techniques**

#### *3.2.1 Balloon-assisted embolization*

DMSO compatible balloon microcatheters with double lumen (Scepter, Microvention Terumo, Aliso Viejo, CA, USA and Eclipse, Balt, Montmorency, France) allow injection of ETOH or NBCA while balloon is inflated within the feeding artery [43, 44]. This creates a wedge positioning of the microcatheter like situation or forms a transient plug to increase the penetration of liquid embolic with minimal or no reflux. This will theoretically decrease the fluoroscopy time and radiation dose and increase the ease of microcatheter removal after injection. This technique is especially effective in fistulous AVMs with large caliber feeders. Balloon inflation prevents reflux and allows a more controlled injection in flow arrest conditions. Special attention must be paid during inflation in order to prevent rupture of the feeder. If there is a problem with balloon inflation, uninflated balloon should be replaced as it may increase the chance of catheter entrapment [45]. If there is reflux along the inflated balloon, further gentle inflation usually prevents reflux. Extreme caution must be paid during inflation of the balloon within the arterial feeders to prevent overinflation and rupture.
