Treatment of AVM: Endovascular Methods

Abstract

In this chapter we review the technical aspects, the indications, and the results of endovascular treatment of intracranial arteriovenous malformation (AVM). From an endovascular perspective, AVM is a hemodynamic vascular area connecting the high-pressure arterial system with the low-pressure venous system by means of arteriovenous shunts. The low-pressure venous system exerts suction on the arterial system and if the arteries supplying the shunts are occluded in a proximal manner, arterial anastomoses develop from adjacent arteries and resupply the shunts. This supports the distinction between proximal embolization that occludes arteries and preserves shunts and distal (or curative) embolization where embolic agent is pushed up to the draining vein. The standard technique of embolization uses the transarterial approach that consists in superselective catheterization of the arterial feeders and injection of embolic agents through microcatheters. Two types of liquid embolic agents are used at Lariboisière: cyanoacrylate (Glubran) and EVOH Copolymer-DMSO solvent (). Glubran is used through perforating and small cortical arteries while Onyx is used through large cortical arteries. Proximal arterial occlusion makes sense only in pre-surgical embolization. On the other hand, when embolization is the sole treatment or when it is performed to reduce the size of an AVM before radiosurgery, the embolic agent must be pushed up to the first centimeter of the draining vein. This venous occlusion carries on a risk of rupture of the shunts if all the arterial feeders going to the shunts have not been first occluded. By transarterial approach, the success of the procedure (defined as an angiographic cure with unchanged neurological examination) depends on several factors that participate to our personal score: perforating arteries (yes = 1, no = 0), en passage arteries (yes = 1, no = 0), watershed area supply (yes = 1, no = 0), size >3 cm (yes = 1, no = 0). A high score is predictive of a poor result. Recently, transvenous embolization has been developed with the help of Onyx. This technique has not been assessed in large series and its hazard is still unknown. We restrict transvenous embolization to small AVM located in very functional area, fed by small arteries with difficult access and drained by an accessible vein. Main risk of any types of embolization is the hemorrhage that occurs when part of the shunts remains patent. The key point concerning the indications of treatment is related to unruptured AVM. Two recent prospective studies using control groups (with patients left untreated) have questioned the benefit of treatment of unruptured AVM. Currently, unruptured AVM are left untreated in their vast majority. Ruptured AVM have a higher risk to bleed than unruptured ones and indications of treatment are larger in such cases. However, when the neurological risk linked to the occlusion of the totality of the arteriovenous shunts is high, we restrict our treatment to the part of the AVM that has been recognized as responsible of the bleeding. Endovascular treatment of AVM is the intervention that requires the longest training in interventional neuroradiology.