Key points

Introduction

With better understanding of the pathophysiology of intracranial dural arteriovenous fistulae (DAVF) and improvement in catheter and embolic material technology, endovascular treatment has become the treatment of choice for most intracranial DAVF. The goal of endovascular treatment of intracranial DAVF depends on clinical presentation, location, and angioarchitecture of the fistula.

DAVF with retrograde leptomeningeal drainage (RLVD) are associated with a high incidence of hemorrhage and symptomatic venous hypertension. Patients who originally present with hemorrhage have a risk of rebleeding as high as 33% in the first 2 weeks. The treatment goal for DAVF presenting with hemorrhage or with progressive symptoms of intracranial or ocular hypertension is complete obliteration. Complete obliteration should be considered even in asymptomatic patients with RLVD, even though lack of symptoms in patients with RLVD is associated with a more benign natural history than in symptomatic patients. There is no evidence to support the notion that partial or palliative treatment reduces the risk of hemorrhage, venous infarction, or visual loss in symptomatic patients with RLVD, although partial treatment may be a reasonable compromise in selected cases. A more individualized approach may be applied to patients with DAVF without RLVD, where symptom amelioration or resolution may be achieved without necessarily obtaining an angiographic cure. This latter principle applies especially to patients with high-flow DAVF without RLVD and severe pulsatile tinnitus interfering with their quality of life.

Careful analysis and understanding of the DAVF angioarchitecture are a critical prerequisite to treatment planning. Pretreatment angiography should address the exact location of arteriovenous shunting, arterial supply (dural and pial), flow characteristics, and venous drainage of the DAVF. Particular attention should be paid to the venous drainage of normal brain during the late venous phase of angiography. The venous outflow should be scrutinized for the presence of a parallel venous pouch or compartmentalization of the involved dural sinus, which is often present in DAVF associated with a major intracranial venous sinus. It is of paramount importance to identify whether the involved sinus is functionally isolated or still serves as a conduit for normal venous drainage.

Complete and persistent obliteration of the DAVF is achieved by occlusion of its proximal venous drainage. Based on the route of access, endovascular approaches to DAVF can be schematically divided into transarterial, transvenous, combined, and percutaneous/direct. The choice of access used depends on clinical presentation, location, ease of access, operator experience, and most importantly, careful analysis of the angiographic architecture of each lesion.

Introduction

With better understanding of the pathophysiology of intracranial dural arteriovenous fistulae (DAVF) and improvement in catheter and embolic material technology, endovascular treatment has become the treatment of choice for most intracranial DAVF. The goal of endovascular treatment of intracranial DAVF depends on clinical presentation, location, and angioarchitecture of the fistula.

DAVF with retrograde leptomeningeal drainage (RLVD) are associated with a high incidence of hemorrhage and symptomatic venous hypertension. Patients who originally present with hemorrhage have a risk of rebleeding as high as 33% in the first 2 weeks. The treatment goal for DAVF presenting with hemorrhage or with progressive symptoms of intracranial or ocular hypertension is complete obliteration. Complete obliteration should be considered even in asymptomatic patients with RLVD, even though lack of symptoms in patients with RLVD is associated with a more benign natural history than in symptomatic patients. There is no evidence to support the notion that partial or palliative treatment reduces the risk of hemorrhage, venous infarction, or visual loss in symptomatic patients with RLVD, although partial treatment may be a reasonable compromise in selected cases. A more individualized approach may be applied to patients with DAVF without RLVD, where symptom amelioration or resolution may be achieved without necessarily obtaining an angiographic cure. This latter principle applies especially to patients with high-flow DAVF without RLVD and severe pulsatile tinnitus interfering with their quality of life.

Careful analysis and understanding of the DAVF angioarchitecture are a critical prerequisite to treatment planning. Pretreatment angiography should address the exact location of arteriovenous shunting, arterial supply (dural and pial), flow characteristics, and venous drainage of the DAVF. Particular attention should be paid to the venous drainage of normal brain during the late venous phase of angiography. The venous outflow should be scrutinized for the presence of a parallel venous pouch or compartmentalization of the involved dural sinus, which is often present in DAVF associated with a major intracranial venous sinus. It is of paramount importance to identify whether the involved sinus is functionally isolated or still serves as a conduit for normal venous drainage.

Complete and persistent obliteration of the DAVF is achieved by occlusion of its proximal venous drainage. Based on the route of access, endovascular approaches to DAVF can be schematically divided into transarterial, transvenous, combined, and percutaneous/direct. The choice of access used depends on clinical presentation, location, ease of access, operator experience, and most importantly, careful analysis of the angiographic architecture of each lesion.

Transarterial embolization of DAVF with Onyx

A transarterial approach has become the most frequently used initial treatment modality for DAVF with RLVD, primarily after the introduction of ethylene vinyl alcohol (Onyx; Covidien, Dublin, Ireland), a permanent, nonadhesive, liquid polymer embolic agent. DAVF with direct RLVD represent the ideal candidates for transarterial treatment with Onyx. DAVF with sinus and RLVD outflow can also be successfully treated with Onyx embolization, especially if a parallel venous pouch or compartmentalization of the involved sinus is present.

A standard transfemoral arterial route is used. An Onyx-compatible microcatheter is navigated and positioned as close as possible to the fistulous connection. The dead space of the microcatheter is filled initially with the solvent dimethyl sulfoxide. A proximal plug of Onyx is then created around the distal tip of the microcatheter to produce sufficient proximal flow arrest and allow distal penetration of Onyx into the fistula. Two separate preparations of Onyx are available: Onyx 18, the agent most commonly used, has low viscosity and allows optimal distal penetration in DAVF with low flow. On the other hand, Onyx 34 has higher viscosity, resulting in greater and more rapid cohesion of the injected material and less fragmentation in the flow stream. The authors use Onyx 34 to build an optimal proximal plug and avoid premature distal migration. A relatively long injection of Onyx will allow optimal DAVF penetration. If a “wedged” distal position of the microcatheter is achieved, Onyx may progress in an antegrade fashion with minimal or no reflux ( Fig. 1 ). If excessive reflux along the microcatheter or inadvertent distal migration of Onyx is noted under fluoroscopy, the injection can be halted, the roadmap renewed, and the injection restarted after 1 to 2 minutes. The goal of treatment is to fill the DAVF proximal venous outlet while allowing retrograde occlusion of contributing arterial feeders, until no shunting is verified on control angiography (see Fig. 1 ).

Incidental tentorial DAVF discovered in an 18-year-old during investigation for a symptomatic vertebral artery dissection. ( A ) Selective right external carotid artery injection demonstrates the fistula ( arrowheads ) fed primarily by the posterior branch of the MMA ( arrows ). The posterior branch of the MMA is an “ideal” branch for catheterization because of its relatively straight course ( black arrows ). ( B ) The straight course of the posterior branch of the MMA allows for a very distal catheterization often in a “wedge” position very close to the point of fistualization ( arrows ). ( C ) Onyx cast showing filling of the “nidus” ( arrowheads ) and the proximal portion of the venous drainage ( arrows ). There is a small amount of reflux around the distal portion of the microcatheter ( white arrows ). ( D ) Selective right external carotid artery injection, late arterial phase, confirms complete angiographic obliteration of the DAVF.

Most noncavernous DAVF are supplied by transosseous branches of the occipital and meningeal arteries, most commonly the middle meningeal artery (MMA). Transosseous pedicles of scalp arteries may be quite tortuous, particularly in their distal course, in proximity to the fistula, and therefore their navigation may be difficult or even impossible. Whenever the posterior branch of the MMA provides a supply to the DAVF, microcatheter navigation and positioning are often possible in close proximity to the fistulous tract (see Fig. 1 ). This branch often provides a natural direct access to the fistula’s venous collector system. Furthermore, the MMA and its branches run a relatively straight course beyond the foramen spinosum, where the artery enters the cranium, and are anchored on the dura, making failed microcatheter retrieval rare despite substantial proximal Onyx reflux. Although proximal Onyx reflux may occur with a high margin of safety in the MMA, reflux should not be allowed in proximity to the level of the foramen spinosum to avoid inadvertent compromise of the arterial supply to the trigeminal and facial nerves. It is therefore important to maintain a lateral view on at least one projection to have an accurate estimation of the level of the skull base.

The most common cause of inadequate fistula obliteration after transarterial Onyx embolization is failure to reach the venous side and/or failure to overfill the proximal venous side. It is important to recognize that Onyx will initially coat the endothelial surface circumferentially before obliterating the lumen of the embolized vessel. The difference may be subtle to differentiate with current angiographic resolution and it is critical to follow the immediate posttreatment angiogram well late into the venous phase to rule out persistent filling. Patients need to have follow-up catheter angiography 3 to 6 months after initial treatment to confirm persistent and complete obliteration because recurrence may develop without associated clinical symptoms. However, long-term occlusion rates seem to be high after transarterial Onyx embolization: in a study of DAVF with initial complete or near complete obliteration, stability of angiographic findings at 6, 12, 24, and 46 months was 100%, 95.4%, 93.8%, and 92.3%, respectively. A lower success rate after Onyx embolization may also be more prevalent after a previously failed embolization.

Several recent studies have confirmed transarterial Onyx embolization to be an effective treatment of DAVF with RLVD. In a single-center prospective series of 30 patients with DAVF and RLVD, 80% experienced angiographic cure, 83% of which after a single procedure. Persistent occlusion was verified in 23 of 24 patients on follow-up angiography at 3 months. Re-hemorrhage, however, occurred in one completely cured patient because of draining vein thrombosis, and one patient developed a transient cranial nerve palsy. Similarly, van Rooij and Sluzewski successfully treated 8 patients with DAVF and RLVD without complications and with complete obliteration present at 6- to 12-weeks follow-up angiography. Puffer and coworkers reported successful complete or near complete obliteration of tentorial DAVF with transarterial Onyx embolization in 8 of 9 patients with no periprocedural morbidity and mortality. Finally, Maimon and colleagues were able to obliterate 94% of DAVF completely with RLVD in 17 patients, with a 6% morbidity.

A distinct disadvantage associated with the use of Onyx for DAVF treatment is the prolonged fluoroscopy frequently used and associated increased radiation exposure. Alopecia and cutaneous burns may therefore develop, while the delayed health risks are currently unknown. In addition, the cost of the procedure may be fairly high. Postprocedural pain is experienced by most patients, probably related to dural ischemia, but is rarely unresponsive to mild oral analgesics. Procedural complications may include inadvertent microcatheter retention, pulmonary embolism, bradyarrhythmia (due to an exaggerated trigeminocardiac reflex), and palsies of the trigeminal, facial, and lower cranial nerves. Arterial ischemic events are rare because dural arteries are the primary conduits used for embolization; however, particular attention should be paid to anastomoses between the external carotid and vertebral arteries that may become more pronounced during the course of embolization. Finally, venous ischemia and/or hemorrhage may result from occlusion of normal cerebral venous drainage.

Transarterial embolization of DAVF with acrylic glue

Transarterial DAVF embolization can be successfully performed with acrylic embolic agents, such as n -butyl-2-cyanoacrylate (nBCA; Trufill, Codman, Raynham, MA, USA), although its use for this indication has decreased in the “Onyx” era, especially in the United States. Patients harboring DAVF with direct RLVD, and less commonly, DAVF with sinus and RLVD, are candidates for this treatment modality. A standard transfemoral arterial route is used. An nBCA-compatible microcatheter is navigated and positioned in close proximity to the fistulous connection in a wedged position with the tip of the microcatheter establishing flow arrest in the vessel. The microcatheter is flushed with a 5% dextrose solution before injection, to avoid glue precipitation within the microcatheter. The injection dynamic should be predicated on the catheter’s distance from the fistula, flow rate, and the size of the feeding artery engaged. Unlike Onyx, nBCA is adhesive and thrombogenic, and recanalization is unlikely to occur if the glue cast traverses the fistulous connection and occludes the immediate proximal venous outflow. Low-concentration nBCA is used to achieve distal penetration in the nidus, and concurrent injection of dextrose solution via the guide catheter during embolization can prevent proximal polymerization and premature proximal occlusion. The angiographic cure rate for DAVF with isolated direct RLVD was shown to improve from 10% to 55% as the mean concentration of glue decreased from 37% to 23%. NBCA embolization offers the advantage of shorter procedure lengths, decreased radiation exposure, and lower cost compared with Onyx-based embolization. Interestingly, delayed thrombosis of incompletely treated DVAF with transarterial acrylics has been reported, presumably because of the thrombogenic properties of nBCA.

Transarterial nBCA embolization may be quite effective even if multiple sessions of transarterial embolization may be necessary for complete DAVF occlusion. Nelson and colleagues reported 30% of cases requiring more than one attempt to occlude the DAVF completely. Although unsuccessful depositions because of inadequate venous penetration may not in and by themselves be curative, they reduce collateral inflow, making subsequent transarterial attempts more likely to be successful in achieving angiographic cure. Complete occlusion was achieved in all patients and no recurrence was encountered during a mean follow-up period of 18.7 months. Angiographic cure was accomplished in 90% (34/38 patients) with DAVF and RLVD with no permanent morbidity, whereas 2.37 arterial pedicles were embolized per patient on an average of 1.37 sessions per patient. In the largest reported retrospective series of 170 patients, treated within a 16-year period, 85% of patients were treated with a single procedure (mean, 1.2 sessions) with a 66% complete occlusion rate (69% complete occlusion in DAVF with RLVD), and 2.3% had a permanent neurologic deficit. Procedural complications during transarterial nBCA embolization are similar to Onyx-based treatment and more commonly include cranial nerve palsies, arterial ischemia, and venous ischemia and/or hemorrhage.