**2.2 Embolization before radiosurgery**

Obliteration rates after radiosurgery decreases as the size of an arteriovenous malformation increases. Obliteration rate decreases from 80 to 50% when the size of the AVM increases from 2.5 to 3 cm [23]. The main aim of embolization before radiosurgery is to decrease the size of the lesion before radiosurgery [24] (**Figure 2**). AVMs larger than 3 cm can benefit significantly by embolization. A successful embolization obliterating the periphery of an AVM can help to decrease the required dose for obliteration and negative effects of the radiosurgery on the neighboring tissues [25]. If an AVM has intranidal aneurysms, these aneurysms can be embolized to decrease the bleeding risk during the latency period. Additionally, targeted embolization can be used to obliterate direct arteriovenous shunts in the arteriovenous malformations to increase the efficiency of the radiosurgery [26].

#### **Figure 1.**

*(A–D) A ruptured choroidal AVM that caused intraventricular and subarachnoid hemorrhage in a 26-yearold male. AVM is supplied by the right posterior cerebral artery (PCA), parietooccipital branch, medial and lateral posterior choroidal arteries, and right pericallosal artery from anterior cerebral artery (ACA). (E and F) Residual AVM supplied by en passage arterial feeders (arrows) from the posterior choroidal arteries and more than 90% size reduction after embolization. These en passage feeders were not amenable to embolization and patient went to surgery for AVM resection on the following day after embolization. Control angiogram after surgical resection does not demonstrate any evidence of a residual AVM (G and H).*

#### **Figure 2.**

*(A and B) An unruptured left perirolandic AVM supplied by middle cerebral artery branches in a 46-yearold female with headaches. (C) Superselective catheterization and angiogram during preradiosurgical embolization. Postembolization angiograms (D) show at least 90% size reduction with a small residual lesion in the Rolandic region. Stereotactic surgery is planned (E) following embolization due to eloquent location. Follow-up angiograms 2 years after radiosurgery (F and G) demonstrate complete obliteration of the AVM without any residual or recurrent lesion.*

There are conflictive reports in the literature regarding the efficiency of embolization before radiosurgery. Whereas some studies have recently mentioned decreased obliteration rates after embolization [27, 28], other studies have demonstrated increased efficacy of radiosurgery with better obliteration rates after embolization [29].

#### **Figure 3.**

*(A–C) An unruptured frontopolar AVM supplied by the orbitofrontal and frontopolar branches of the right ACA and drained by a single frontal cortical vein into the superior sagittal sinus. (D) The ETOH cast after embolization of two feeders in the same session with a curative intent. ETOH cast completely matches with the angioarchitecture of the AVM. Final angiograms (E and F) show complete obliteration of the AVM without any residual filling.*

In our practice, we recommend embolization before radiosurgery for cases with a volume larger than 10 cc, fistulous arteriovenous shunting, and intranidal aneurysms.

## **2.3 Curative embolization**

Complete obliteration rates with embolization have been reported between 9.7 and 14% with NBCA (N-butyl cyanoacrylate) [30]. During the Onyx era, complete obliteration rates with stand-alone embolization rose up to 18–51% [31]. Even higher cure rates up to 94% has been reported in smaller series with selective cases [32]. There were higher rates in AVMs with smaller size and a smaller number of arterial feeders (**Figure 3**). AVMs that have less prominent angiogenic nidus and predominantly fistulous AVMs compared to pure plexiform lesions were also more prone to complete obliteration. Small AVMs with single or less than two feeders with deep and central location are good candidates for stand-alone endovascular treatment. Larger size of the feeding artery also increases the chance of complete angiographic obliteration [33]. According to Valavanis and Yasargil, sulcal AVMs fed by pial arteries are more amenable to safe and effective embolization [34]. Most recent meta-analysis by Wu et al. [31] found an overall complication rate of

#### **Figure 4.**

*(A) Ruptured cerebellar AVM supplied by the left anterior inferior cerebellar artery (AICA) branches and with drainage into the left transverse sinus. (B) A flow-related aneurysm on the left AICA and multiple intranidal aneurysms. Unsubtracted angiogram (C) after targeted embolization of the left AICA shows NBCA cast within the aneurysm that was most likely the culprit for the previous rupture and hemorrhage. Postembolization angiogram before surgery (D) shows occlusion of multiple aneurysms with residual AVM.*

24.1% including hemorrhage occurring in 9.7% of patients and procedure-related mortality rate of 1.5%. These rates are slightly higher compared with studies where the goal was adjunctive embolization before surgery or stereotactic radiotherapy. Even though stand-alone embolization with intent to cure has the potential to be a safe and efficient treatment, it must be preserved for select AVM cases or can be welcomed as an unanticipated result of an adjunctive endovascular treatment.
