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100% in recent years (23, 36, 39). However, in the case of transverse–sigmoid sinus dural arteriovenous fistulae (TSDAVFs), the rate was lower than 40% because of its complex anatomic factors (35).
heard by the patient or by auscultation over the mastoid, may be an indication for magnetic resonance imaging or angiography (3, 59, 60). Conventional magnetic resonance imaging is often positive in DAVF with retrograde cortical venous drainage or retrograde flow in the venous sinus with venous congestion. DAVFs with retrograde cortical venous drainage or retrograde flow in the venous sinus with venous congestion often has prominent flow voids on the surface of the brain. High-intensity lesions in the deep white matter on T2-weighted images are secondary to the venous hypertension and venous congestion (Figure 1). The combination of prominent flow voids on the surface of the brain and high-intensity lesions in the deep white matter on T2-weighted images is highly suggestive of a DAVF (48).
CLINICAL PRESENTATION OF DAVFS
ANATOMY
Patients with TSDAVFs may present with subjective pulse-synchronous tinnitus, bruit, insomnia, headache, visual decline, seizure, and/or altered mental status, including dementia (3, 41). The most common symptoms of TSDAVFs were pulsatile tinnitus (81% of cases), headaches (15%), and intracranial hemorrhage (10%) (21, 25). Even trigeminal neuralgia has been reported (11). However, a history of pulsatile tinnitus was reported in 50% of the case reports of trigeminal neuralgia caused by a DAVF (11). Dural AVFs can also result in life-threatening brain edema, hemorrhage, and venous infarction (24, 37, 57). Those with a retrograde leptomeningeal venous drainage are regarded as high-risk, having the potential to hemorrhage and result in serious neurologic complications requiring urgent treatment (27). Neurologic dysfunction is thought to be due to venous hypertension, with resulting venous ischemia or hemorrhage (43, 58). Drainage of the fistula into cerebral surface veins, as opposed to dural sinuses, probably predisposes to an aggressive course and merits surgical or endovascular therapy. Pulsatile tinnitus,
The transverse sinus extends from the confluence of sinuses to the opening of the superior petrosal sinus, beyond which it continues as the sigmoid sinus and then the jugular bulb. The transverse sinus always has venous cranial afferents, whereas the sigmoid sinus never receives cerebral veins. The potential for retrograde leptomeningeal venous drainage evolving in these locations is therefore not the same. Septations may occur within the dural sinuses and result in separate venous channels, which may run parallel to each other (5). On occasion, one of these channels may be draining the brain while the other is exclusively used for drainage of the DAVFs, providing a specific target for treatment (56). TSDAVFs have two types of arterial suppliers (6, 30). The first type is transosseous arterial supply, which is mainly tortuous and multiple and comes from a single arterial trunk, normally the transosseous branches of the occipital artery and/or superficial temporal artery. In addition to representing the main path for most of the blood flow for the DAVF, it is also difficult to perform superselective catheterization of
Transverse–sigmoid sinus dural arteriovenous fistulae are abnormal arteriovenous communications within the dural wall of the transverse–sigmoid sinuses. They present with a variety of clinical features, ranging from benign bruits to intracranial hemorrhage and neurologic deficits. The presentation and natural history of these fistulae are largely determined by the pattern of venous drainage. Knowledge of natural history and careful study of the angioarchitecture by angiography is therefore mandatory for correct management of these lesions. In this review, anatomy and pathology, principles of management, and the various factors that influence treatment decisions are discussed, with a focus on endovascular therapy. Indications for endovascular treatment, therapeutic goals, approaches, and techniques are reviewed. The role of surgical treatment is also briefly discussed.
INTRODUCTION Dural arteriovenous fistulae (DAVFs) consist of arteriovenous fistulae of blood confined within dural leaflets (51). Studies have shown the crude risk of hemorrhage for DAVF to be 2% per year (7). The most common locations of dural arteriovenous malformations (DAVMs) are the transverse and sigmoid venous sinuses (56). The endovascular cure rate of DAVF involving other locations (e.g., tentorium or cavernous sinus) has been dramatically improved up to 80%– Key words 䡲 Arteriovenous fistula 䡲 Transverse–sigmoid sinus Abbreviations and Acronyms AV: Arteriovenous DAVF: Dural arteriovenous fistula DAVM: Dural arteriovenous malformations NBCA: N-butyl cyanoacrylate TSDAVF: Transverse–sigmoid sinus dural arteriovenous fistula TSS: Transverse–sigmoid sinus From the Beijing Neurosurgical Institute, Beijing Tiantan Hospital, Capital Medical University, Beijing, People’s Republic of China To whom correspondence should be addressed: Zhongxue Wu, M.D. [E-mail:
[email protected]] Citation: World Neurosurg. (2010) 74, 2/3:297-305. DOI: 10.1016/j.wneu.2010.02.063 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2010 Elsevier Inc. All rights reserved.
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Figure 1. A, T2-weighted image. Diffuse white matter hyperintensity is seen in occipital lobe on the left side. B, Left external carotid angiogram shows the dural arteriovenous fistula (DAVF) fed by posterior auricular artery with drainage into the left isolated sigmoid sinus. Note reflux into
this transosseous arterial supply. The second type of vascularization for TSDAVFs is meningeal, the petrosquamous branch of the middle meningeal artery is frequently recruited in TSDAVFs of the transverse– sigmoid sinus. Although the meningeal arterial system may appear to be a supplementary afference network for DAVFs (Figure 2), it provides a natural access to the venous collector system of these lesions (30). Contrary to the transosseous arterial supply, the meningeal arterial system penetrates the cranium through the base, thus making the anatomy more navigable and, consequently, more favorable to microcatheterization (Figure 3).
PATHOGENESIS TSDAVFs may be of either congenital or acquired origin. Congenital lesions are much rarer and thought to develop in the first trimester as a result of persistent communication between future arterial and venous segments of the primitive vascular plexus as the intervening capillary network fails to develop (22). Sinus thrombosis and increased venous pressure are recognized contributors to the development of acquired TSDAVFs (20). Nishijima et al. (46) reported a 72% rate of sinus thrombosis concomitant with TSDAVFs. In experimental models, increased venous pressure associated with sinus thrombosis and venous outflow obstruction resulted in the opening
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the cortical veins, occlusion of the left sigmoid sinus and severe stenosis of the left transverse sinus. C, Left external carotid angiogram obtained after transarterial embolization shows that the DAVF was completely obliterated and there is no reflux into the cortical veins.
of preexisting arteriovenous (AV) fistulae in the normal dura mater (22). Ishikawa et al. found that normal AV fistulae exist within the dura and DAVFs may subsequently evolve from these normally occurring fistulae if the conditions are favorable (22). Congenital factors, namely the persistence and enlargement of primitive dural arteriovenous communications that normally involute during development, are thought by some authors to be causal. The occurrence of DAVFs during childhood, however, is rare. When they do occur in children, these lesions tend to be complex and bilateral, occur more often in male patients, and are associated with cardiac failure and a high mortality rate (38%) (2). Arnautovic et al. (2), in their comprehensive meta-analysis, outlined three possible stages in the natural history of DAVMs: 1) sinus thrombosis with engorged dural venous collaterals and the opening of embryonic arteriovenous communications; 2) arteriovenous shunting, which favors the recruitment of arterial feeders into the nidus with secondary venous hypertension; and 3) leptomeningeal retrograde venous drainage, with possible subsequent varicose and aneurysmal dilation. Hamada et al. (16) hypothesized that the venous hypertension in patients with DAVMs is based on two factors: 1) the increased blood flow through the draining vein caused by a direct shunt into this vein and 2) the restricted venous outflow, which arises distal to the DAVMs because of the
increased blood flow, elevated pressure, and turbulence in the draining vein. According to Hamada et al. (16), these stresses combine to restrict the venous outflow and, in turn, decrease cerebral compliance, elevate intracranial pressure, and even cause hydrocephalus in some patients (2). If blood flow through existing dural AV fistulae increases because of sinus thrombosis, trauma, or sinus or venous hypertension, AV fistulae may develop into DAVFs. Thus, the involvement of AV fistulae in the normal dura mater in the etiology of DAVFs cannot be ruled out (22). It might be postulated that sinus hypertension, caused by stenoocclusive disease of the venous sinuses (at least in some cases), and arterial hypertension force open abnormal connections between arteries and veins in the dura mater, which may result in increasingly dilated venules and the formation of DAVFs (22). After such an abnormal arteriovenous fistula has been formed in the wall of the venous sinus, thickening and stenoocclusive sinus lesions ensure that the fistula also recruits arterial blood from numerous dural and, later, pial arteries. Increased sinus pressure promotes the progression of the disease process, and thus a vicious cycle might be created (19).
PATHOPHYSIOLOGY Histopathologically, DAVFs consist of multiple abnormal direct communications (so
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Figure 2. A 55-year-old man presented with intracranial hemorrhage. A, Computed tomographic scanning shows a hematoma in the right temporooccipital lobe. B, Right external carotid angiogram, lateral projection, showing a transverse–sigmoid sinus dural arteriovenous fistula of Cognard type III the right transverse sinus (TS) draining superiorly into the dilated Trolard vein
called crack-like vessels) between dural arteries and dilated dural veins without an intervening capillary bed (22). This lesion is located most frequently at the transverse– sigmoid junction. Most DAVFs occurred at ages 40 – 60 years. Location and venous drainage pattern are two parameters that determine the clinical presentation (11). In DAVFs with antegrade flow obstruction and reflux into the superior sagittal sinus, straight sinus, or cortical veins, the retrograde transmission of pressure results in intracranial venous hypertension. This venous hypertension and the resultant congestion in turn impair parenchymal venous drainage, thereby causing ischemia (43). Hamada et al. (16), who studied nine patients with DAVFs, suggested that the development of an abnormal communication between dural arteries and veins was an essential factor in the pathogenesis of DAVFs.
(arrows) to the superior sagittal sinus and draining inferiorly into the tentorial sinus (arrowheads) to the right TS. C, Catheterization of the right middle meningeal artery. D, Allowed injection of 2 mL of Onyx in right middle meningeal artery and 1 mL in right occipital artery, with retrograde occlusion of other feeders. E, postoperative 3-month assessment shows complete fistula cure.
The diameter of the AV fistulae in our series ranged from 30 to 80 mm. The reported diameter of DAVFs was approximately 200 mm (47). Because AV fistulae exist in the normal dura mater, they may be the origin of DAVFs. The essential abnormality was not a direct arteriovenous shunt to the sinus lumen but a connection between dural arteries and dural veins within the venous sinus wall (22). Thickened walls of the artery and vein, with smooth muscle cells, probably indicate that there has been high blood flow for a long time. In addition, the internal elastica lamina of dural arteries in DAVF cases tended to be stratified.
CLASSIFICATION Although a topographic classification of DAVFs according to location may be use-
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ful in planning a therapeutic approach, from a clinical viewpoint it is more appropriate to classify these lesions according to their venous drainage pattern. In 1978, Djindjian and Merland (12) presented a classification of DAVFs according to the venous drainage (Table 1). Additional classifications were proposed by Borden (4) (Table 2). Later, Cognard et al. (7) modified this classification and correlated between clinical presentation and angiographic findings (Table 3). They all emphasize the venous outflow characteristics of DAVFs and their relationship to presentation. It is of paramount importance to distinguish fistulae with and without retrograde leptomeningeal or cortical venous drainage. The natural history of these two groups of dural fistulae is different and therefore they require different management strategies.
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Table 2. Borden Classification of DAVFs (1995) 1. Venous drainage directly into dural venous sinus or meningeal vein 2. Venous drainage into dural venous sinus with CVR 3. Venous drainage directly into subarachnoid veins (CVR only) CVR, cortical venous reflux; DAVF, dural arteriovenous fistulae.
present with brain-stem ischemia and myelopathy.
Timing of Treatment Patients who present with intracranial hemorrhage or neurologic deficit with retrograde leptomeningeal reflux should be managed aggressively. There is evidence that rebleed may occur early after presentation (66) and we recommend that treatment be carried out soon after the diagnosis. Endovascular treatment, which under these circumstances may require several stages, has to be curative.
Figure 3. Left common carotid angiogram (A) shows the fistula is supplied by the left middle meningeal artery, the left postauricular artery and the left occipital artery and drains into the vein of Labbé. B, Under roadmapping, the microcatheter was advanced to the fistula point via the left middle meningeal artery (arrowheads). C, Postembolization angiogram of the left external carotid artery reveals complete embolization of the fistula. D, After embolization, the fluoroscopic image, lateral view, demonstrated the Onyx cast (arrow).
Natural History In previous studies (3, 12), the aggressive to nonaggressive ratio was 1:8.8 for fistulae into the transverse or sigmoid sinus. An aggressive behavior was found in 40%, 30%, and 70% of Merland type IIa, IIb, and IIa⫹b fistulae, respectively, and in 80% and 95% of types III and IV, respectively. Bleeding was seen in 20% of type II lesions, and in 40% and 66% of types III and IV, respectively. In an updated review of 118 patients of DAVFs with leptomeningeal reflux, the Toronto group demonstrated an annual risk of 6.9% for nonhemorrhagic neurologic deficit, 8.1% for hemorrhage, and an annual mortality rate of 10.4% (66). These data support the need for active and curative treatment of DAVFs when associated with leptomeningeal and/or cortical venous reflux and conservative management in those
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DAVFs that do not have such venous drainage. Dural transverse sinus arteriovenous fistulae with cortical venous drainage were associated with a high hemorrhagic risk of 10%– 40% and significant morbidity and mortality (29). In cases with associated spinal perimedullary drainage, they might Table 1. Djindjian Classification of DAVFs by Venous Drainage (1978) Type I
Drainage into a sinus
Type II
Sinus drainage with reflux into cerebral veins
Type III
Drainage solely into cortical veins
Type IV
With supra or infra tentorial venous lake
DAVF, dural arteriovenous fistulae.
TREATMENT Spontaneous regression of TSDAVFs is relatively rare (maximum 5% of patients) and usually occurs following a hemorrhage (35). The indication to treat a TSDAVF in the presented series was related to relevant clin-
Table 3. Cognard Classification of DAVFs (1995) I. Venous drainage into dural venous sinus with antegrade flow IIa. Venous drainage into dural venous sinus with retrograde flow IIb. Venous drainage into dural venous sinus with antegrade flow and CVR Iia⫹b. Venous drainage into dural venous sinus with retrograde flow and CVR III. Venous drainage directly into subarachnoid veins (CVR only) IV. Type III with venous ectasias of the draining subarachnoid veins CVR, cortical venous reflux; DAVF, dural arteriovenous fistulae.
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ical symptoms (e.g., pulsatile tinnitus) and/or to angiographic findings such as cortical venous drainage. In the beginning of the 1990s, because the experience with intracranial coil placement was limited, the predominant endovascular procedure to treat TSDAVFs was transarterial embolization. Feeding artery embolization of external carotid artery branches with particles (polyvinyl alcohol) or liquid embolic agents (N-butyl cyanoacrylate [NBCA]) is easily performed and may reduce the arteriovenous shunt. However, complete cures are sometimes difficult to achieve with this method because of the existence of feeding arteries that cannot be catheterized and the recruitment of blood supply from collateral arteries. Therefore, this approach is mostly used to relieve symptoms or in combination with other procedures such as transvenous embolization, surgery, or irradiation. In the time before Gugliemi detachable coils came to be used, Halbach et al. (15) reported on 17 patients who had transarterial embolization using a variety of occlusive agents, primarily NBCA, and 10 (59%) of these patients were cured. Liebig et al. (30) treated 33 patients with transarterial embolization alone. The long-term occlusion rate is not greater than 30%; 46% of these patients were clinically cured and another 36% showed symptom relief, whereas the patients with intracranial hemorrhage remained clinically unchanged. As an alternative option in the management of type II dAVFs, da Costa et al. (10) describe a series of 23 patients with surgical/endovascular disconnection only of the cortical venous reflux and preservation of the sinus in order to convert it into a type I fistula. They saw no further hemorrhagic event or neurologic deterioration during a follow-up period of almost 5 years. The surgical procedure was associated with permanent complications in only two cases (8% complication rate), including one visual field defect that was most likely due to the hemorrhage at presentation (10). Terada were early proponents of venous sided treatment of dural arteriovenous malformations and advocated them as a safe and effective alternative to transarterial or surgical techniques (62). Growing experience with transvenous procedures and the availability of improved microcatheters and coils (e.g., fiber coils) modified the therapeutic strategy by using the transvenous ap-
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proach more and more as the primary therapy and transarterial embolization as an additional option for residual arterial feeders only. In a transvenous group, the postinterventional angiography showed complete occlusion of the fistula in 81%, and at discharge from the hospital 91% were clinically cured. Follow-up angiographies showed thrombosis of residual fistulae and no recurrence of the fistula. Because delayed thrombosis of residual arterial feeders was observed while preparing an additional transvenous procedure, it is worth waiting some weeks after transvenous packing of the sinus and to carry out a late control angiography. It became apparent that dense transvenous coil packing of the entire sinus segment involved in the arteriovenous shunt resulted in complete obliteration of the fistula without transarterial embolization. Nevertheless, the majority of TSDAVF patients in our hospital underwent a combination of transarterial and transvenous procedures, whereas in many cases one or more transarterial procedures preceded the transvenous access because until now it was established practice to reduce arterial inflow prior to transvenous occlusion. Nevertheless, packing of a venous sinus involved in the drainage of normal brain tissue may result in catastrophic complications (venous hemorrhage) (35, 55). We have encountered two patients who died of this after sinus packing. We favor starting with the arterial approach, using a permanent embolic agent such as Onyx-18 (ev3, Irvine, CA, USA) after the year 2004. The characteristics and properties of Onyx-18 have shifted the paradigm in the treatment of intracranial DAVFs, especially when this agent is released in the interior of the diseased venous collector system located along the sinus wall, allowing for complete exclusion of the lesion in just one session. The algorithm shown in Figure 4 will be helpful in selecting treatment modalities in the case of a DAVF. Onyx-18 is a precipitating liquid embolic agent. Limited reflux of the slowly solidifying agent around the distal end of the microcatheter creates a wedged position, which may allow for a far distal penetration even if injected from a relatively proximal position (9, 38, 63). Cure of DAVFs at various sites using transarterial Onyx embolization has been reported (33, 34). The ability to occlude different feeders from a single pedicle cathe-
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terized for injection is known and especially useful in DAVFs with limited direct venous access. Theoretically, transarterial embolization with subtotal occlusion of the fistula is very effective in reducing the impact of shunting to the venous circulation and should relieve the patient’s symptoms as well as decrease the potential risk of intracranial hemorrhage or ischemia. In recent studies with a combination of transarterial embolization, radiosurgery, and microsurgery, relatively high obliteration rates between 58% and 83% had been achieved (32, 53), which could partially be explained by late-onset thrombosis of DAVF after incomplete embolization. Recently, some authors reported on the use of stent placement in the treatment of TSDAVFs in a small number of patients (18, 30, 44). Theoretically, transient balloon dilatation and the persistent radial force of an oversized stent may compress pouches within the sinus wall where the arteriovenous connections are located and restore orthograde flow even in chronically occluded sinuses. Although some cases have been successfully treated with stents, the long-term results are not yet known. Stenting of the sinus failed to reduce the arteriovenous shunt if irregular narrowing of the sinus segment prevented complete opening of the self-expanding stent even after balloon angioplasty. Furthermore, self-expanding stents with a sufficient diameter are relatively stiff. Therefore, it may be difficult to introduce such a stent into the affected sinus segment if there is an acute angle between the internal jugular vein and the sigmoid sinus. Today, we consider stent deployment as a treatment option in patients where transvenous occlusion of the sinus is contraindicated and orthograde blood flow has to be maintained or restored.
Indications and Strategy The appropriate use of therapeutic options, which include conservative management, endovascular therapy, and surgery, depend on multiple factors. As a general principle, therapeutic strategy will be based on the pattern of venous drainage, since it determines the natural history of the DAVF.
No Reflux The indications for treatment of DAVFs, which drain directly into a dural venous si-
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Figure 4. Algorithm for the treatment of dural arteriovenous fistulae (DAVF).
nus with normal antegrade flow, are limited. Elective intervention aimed at symptom reduction may be required occasionally when tinnitus or headaches are not well tolerated by the patient (Figure 5). The treatment-associated risk will then have to be weighed against the very low risk of the disease itself (56). Treatment options for dural AVFs involving the TS sinus include intermittent occipital artery compression, transarterial embolization. Transarterial embolization of TSDAVFs alone is indicated in patients without a risk of intracranial hemorrhage (type I drainage) as a symptomatic treatment with a low complication rate. Transarterial embolization with Onyx-18 is useful in reducing AV fistulae but it is less likely to achieve clinical cure. Only when liquid embolic materials occlude the AV fistulae properly is clinical cure obtained. Because complete obliteration of the AV fistulae with glue is not always possible, recanalization and collateralization may occur (55). Transarterial embolization following radiosurgery may provide immediate symptom relief and may be effective during the latency period of radiosurgery (13). The risk associated with the use of Onyx in treatment of TSDAVFs is excessive venous passage (33). The risk in these sinustype DAVFs was migration of Onyx from the sinus to the arterialized draining veins, which may cause distal venous occlusion and consequent venous infarction or hemorrhage. In the present cases, Onyx migrated into the right cardiac ventricle via the internal jugular vein.
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Reflux Through the Sinus Because of distal venous obstruction, DAVFs draining into the transverse sinus may be associated with retrograde flow toward the opposite side and reflux upstream to the superior sagittal sinus or the straight sinus and deep venous system (10). Treatment of such DAVFs is indicated but can be challenging. Arterial embolization followed by transvenous disconnection of the involved dural sinus has proven to be the most efficient treatment method. A high-flow DAVF creates a physiologic obstruction to drainage of the normal brain, which in turn may produce clinical symptoms and require active treatment. Under these circumstances, treatment should always be directed toward the arterial side of the lesion in order to preserve the dural sinus and lower the venous pressure, enabling the brain to use this sinus again for its drainage (56). The management of fistulae where the venous drainage combines cortical venous reflux and sinus involvement (Borden type II) is more complex. Direct surgical treatment frequently involves complex surgical procedures and significant blood loss (14, 52). Occluded sigmoid sinus distally could make the transvenous approach difficult (26). Naito et al. (45) presented a type IV fistula treated by a transvenous route, via an occluded jugular vein. They passed the occluded segment with a Terumo 16 guidewire and 5F diagnostic catheter. The classical technique of percutaneous transvenous
embolization through the occluded sinus for TSDAVFs with sinus occlusion was described by Naito et al. (45). In Naito et al.’s case series of six patients, they were able to access through the occluded sinus in five (83%) patients and achieve an angiographic cure in four (67%) patients. The remaining two patients went on to surgical excision and direct packing of the isolated sinus, respectively. The technique that Naito et al. employed was to catheterize the occluded segment with a stiff 0.035-inch guidewire with rotation and advancement. A roadmap was then generated by pulling out the stiff guidewire. The same route was then advanced with microcatheter, guided by the roadmap. The affected sinus was packed using Guglielmi or interlocking detachable coils or fiber coils. Hanaoka et al. (17) described a variation of the above-mentioned technique involving the use of a gooseneck snare to pull the microguidewire to advance the microcatheter through the occluded sinus. They performed the same maneuver up to the point of passing the catheter under the roadmap guidance. The attempted catheter was a 0.038-inch microcatheter (Tracker 38; Target Therapeutics/ Boston Scientific, Fremont, CA, USA) over the microguidewire (Transend-14; Target Therapeutics/Boston Scientific). A contralateral approach beyond a confluence is effective in patients with occlusion of the ipsilateral jugular vein. Navigation of the microcatheter beyond the midline is easy in patients when the shape of the confluence is a reversed T-shape. However, it is difficult when the confluence has a reversed Y-shape because the angle between the transverse sinuses is acute. A 5F guiding catheter with side hole enabled the microcatheter and the microguidewire to turn at a sharp angle and served as a stable guiding base to override the sharp angled confluence without any kickback of the catheter (64). Rivet described a technique of access by percutaneous puncture through a mastoid emissionary vein (54). This would certainly be a useful adjunct when feasible. Soft-tissue hemorrhage, which may be profuse because of the abnormal vascularity, should be managed meticulously. In the two patients that we described, we were able to catheterize along the presumed path of the occluded sigmoid sinus with microguidewire and microcatheter without the use of a stiff guidewire. We attributed our success to
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Figure 5. A 28-year-old man presented with intracranial bruits caused by a left sigmoid sinus dural arteriovenous fistula (DAVF). The fistula was supplied by feeders from the ipsilateral external carotid artery. The left external carotid angiograms (A) show a left sigmoid sinus DAVF (Cognard type I). The DAVF was incompletely obliterated with a single Onyx injection through the left occipital artery. B, The examination of thoracic x-ray films, lateral view, shows the Onyx fraction in right heart ventricle.
being able to maintain a support of the 1.9F microcatheter from the 6F guiding catheter in the sigmoid sinus–internal jugular vein junction and a supporting length of microguidewire upstream of the occluded sigmoid sinus. Other interesting variation would be embolization of the parallel venous channel with preservation of the parent sinus, if the existence of a parallel venous channel as the recipient pouch for all arterial inflow was identified (28). Transarterial embolization of TSDAVFs is safe and effective in patients with sinus reflux with a low complication rate. The goal of transarterial embolization of TSDAVF is the obliteration of all feeding arteries, the proximal obliteration of eventually present cortical draining veins together with the preservation of the patency of the affected transverse–sigmoid sinus. To achieve this with Onyx-18 injection is possible; sufficient penetration of the fistula could be achieved in the majority of cases, and proximal venous passage requires injection of the liquid embolic from a wedged microcatheter position (1, 31). The conversion of a malignant type II DAVF in a benign type I is intuitively attractive (50).
Reflux Straight into a Cortical Vein Indications for treating DAVFs with direct retrograde leptomeningeal venous drainage are now well established, and a cure must be obtained to prevent future hemorrhage or neurologic deficits (10). Kong et al.
(28) described a series of patients treated with direct packing with interlocking detachable coils of the isolated sinus, in DAVFs of the transverse–sigmoid sinus, through a small 4- ⫻ 2-cm craniotomy; one patient died. Access to the isolated transverse–sigmoid sinus from the contralateral side was described by both Halbach et al. and Komiyama et al. (27). Komiyama et al. described 2 cases with access from the contralateral sigmoid–transverse sinus. Because of the length and tortuosity, lack of pushability over the torular herophili might be encountered, as in one of Komiyama’s cases. A triaxial system (instead of a coaxial system) would provide better support and overcome the access problem (61). The limitation of the technique would be cases with isolated transverse sinus, as in the two illustrated cases (67). DAVFs involving the isolated sinus are classified as being of the Cognard type IIb, though their retrograde leptomeningeal venous drainage pattern is more reminiscent of types III and IV. In the Boden classification, they are classified as type III. Urtasun et al. (65) reported vessel perforation of the sigmoid sinus during attempted transvenous catheterization passing through the occluded sinus. When the venous drainage is cortical, the arterial approach is usually performed and a liquid emboligenic agent is used (49, 53). Transarterial navigation allows, in a single approach, a sufficiently distal access for the tip of the microcatheter and the injection of a liquid emboligenic agent. Onyx-18 was in-
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troduced as a liquid embolic agent for DAVF embolization and is characterized by a different solidification process consisting of a copolymer precipitation instead of NBCA polymerization. Compared with NBCA, Onyx-18 allows for slower and longer injection rates, which can be better controlled (23, 42, 34, 40). Furthermore, because of its nonadhesive nature and penetration characteristics, Onyx-18 is a promising embolic agent for endovascular treatment of DAVMs with isolated sinus. In our opinion, this is transarterial embolization first and if incomplete to be followed by stereotactic radiosurgery. The results are preliminary but appear to be encouraging for this particular indication (13).
Complications of Embolization Reported anatomic cures range from 70% to 88% of patients treated by arterial or venous or combined endovascular approaches (35, 56). The potential hazards of arterial embolization of DAVFs are related to the neurologic territories of these feeders, their potential anastomoses to the intracranial circulation, and their blood supply to the transcranial nerves. Such complications should be avoidable with thorough knowledge of the vascular anatomy and their variations described in the literature. The position of the tip of the microcatheter and the type of embolic material chosen should be selected with this risk in mind. In our opinion, there is no additional benefit from provocative injection of certain drugs (e.g., barbiturate) if the above guidelines are followed. The risks associated with the retrograde transvenous approach are, other then vessel perforation, mostly related to the underestimated effect that the dural sinus sacrifice might have on the venous drainage of the cerebral and cerebellar circulations. Literature series of transvenous (with or without transarterial) procedures reported complication rates between 10% and 42% (30, 53). Transient neurologic deficits have been reported in 4%–33%, permanent neurologic deficits in 4%–5% and mortality in 0%– 4% (56). Our overall complication rate was 5.3% (35).
Follow-Up Cognard et al. (8) reported that seven patients with DAVF showed an alteration in
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the initial type of venous drainage to one with a higher grade during long-term follow-up. They suggested that any change in the clinical picture is an indication for a repeat digital subtraction angiography, and stenosis of the venous drainage, indicating later worsening of the venous outlet, requires more thorough angiographic follow-up (48).
CONCLUSION The clinical presentation and natural history of DAVF is now better understood and is largely determined by the venous outflow characteristics of the lesion. Retrograde venous drainage into leptomeningeal and/or cortical veins is strongly predictive for intracerebral hemorrhage and neurologic deficits. Patients with initial presentation with intracerebral hemorrhage or neurologic deficit require aggressive management aimed at cure. Conversely, the natural history of TSDAVF, which drain directly into a dural venous sinus with normal antegrade flow is benign. Treatment is therefore rarely indicated, except occasionally to relieve symptoms of tinnitus. The use of Onyx-18 with a transarterial approach via the meningeal arterial system is now frequently used as the first treatment for TSDAVFs, and complete cure is possible. Onyx arterial embolization may be performed as an alternative to retrograde venous catheterization. A combination of arterial, venous, and surgery as well as radiosurgery, if necessary, is then indicated to prevent intracranial hemorrhage. Radiosurgery is a choice when a complete cure is the goal, but endovascular techniques fail to be curative or are technically not feasible.
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Conflict of interest statement: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. received 07 January 2010; accepted 12 February 2010 Citation: World Neurosurg. (2010) 74, 2/3:297-305. DOI: 10.1016/j.wneu.2010.02.063 Journal homepage: www.WORLDNEUROSURGERY.org
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