Cognard classification of dural AVS (1995)
Intracranial dural arteriovenous fistulas (DAVFs) represent 10 to 15% of intracranial arteriovenous malformation. [1-3] Published classifications of DAVFs (e.g., Cognard′s classification) are based on the pattern of drainage, for estimation of bleeding risks.  Venous drainage patterns allow classification of DAVFs into five types as follows: Type I, located in the main sinus, with anterograde flow; Type II, located in the main sinus, with reflux into the sinus (Type IIa), cortical veins (Type IIb), or both (Type IIa+b); Type III, with direct cortical venous drainage without venous ectasia; Type IV, with direct cortical venous drainage with venous ectasia; Type V, with spinal venous drainage (Table1). Depending on the DAVFs location and the venous drainage, clinical presentations range from asymptomatic to symptomatic [5-11], with pulse-synchronous bruit, headaches, neurological deficits, venous hypertensive encephalopathy with dementia, or intracranial hemorrhage resulting from venous hypertension.
The decision to treat is based on the venous drainage pattern, the natural history of the lesion, the severity of presenting symptoms, the patient′s general condition, angiographic features, the location of the DAVF, and the morbidity and mortality rates of the procedure being considered. The goals of treatment are the prevention of risks and the elimination of symptoms caused by the arteriovenous shunt. Because of the bleeding risk, intracranial DAVFs with retrograde cortical drainage often require an anatomic cure. They can be treated with different modalities, such as endovascular procedures with transvenous and transarterial [2, 3, 5, 11-36], surgery [6-8, 35, 37-43], gamma knife surgery [31, 44-47], or combinations of the three [7, 24, 48-50]; in selected cases, the lesions can be treated conservatively .
2. Transvenous technique
The embolization of DAVFs is performed under general anesthesia, preferably under supervision of an experienced neuroanesthesiologist. Transvenous catheterizations and embolizations are often lengthy procedures (2–4 h), during which the typically elderly patients would have difﬁculties remaining still on an angiographic table. General anesthesia with endotracheal intubation is therefore widely used in most centers in the world, as it also allows for safer monitoring and easier management in cases of intraprocedural complications such as rupture and hemorrhage. Bilateral selective internal carotid artery (ICA) and external carotid artery (ECA) angiography and vertebral artery (VA) angiography were performed for all patients, for assessment of the feeding arteries, the fistula sites and the venous drainage. The arteriovenous shunts were approached via the venous route. We first placed 6-French sheaths in the femoral artery and vein. A 5-French catheter in the carotid artery allowed observation of the shunt, acquisition of roadmaps, and angiographic monitoring of the procedure. A second 5-French catheter was placed in the jugular vein. A microcatheter (Marathon/Echelon, MTI-EV3, Irvine, CA, USA) was navigated coaxially via different venous approaches. The microguiderwire (Mirage/Silverspeed10, MTI-EV3, Irvine, CA, USA; Transend0.014, Boston Scientific, USA) was then carefully introduced and advanced to the fistula portion, followed by the microcatheter. Subsequently, the draining vein or sinus was packed using detachable platinum coils or a combination with Onyx, using real-time digital subtraction fluoroscopic mapping.
3. Case reports (Figs.1-8)
3.1. Case report I: Ethmoidal DAVF (Fig.1)
A 48-year-old man with a DAVF of the anterior ranial fossa supplied by branches of the anterior ethmoidal arteries, the septal branches of the sphenopalatine and the middle meningeal arteries with venous drainage via dilated frontopolar veins to the superior sagittal sinus. A guide catheter was inserted into the jugular vein transfemorally and a microcatheter (Echelon10, MTI-ev3, Irvine, CA) was navigated over a guidewire (Silverspeed, MTI-EV3, Irvine, CA, USA) to the frontal part of the superior sagittal sinus. The microcatheter was gently advanced into the primary draining vein. Once the tip of the microcatheter had reached the fistula point, embolization was performed with detachable platinum coils until transarterial angiography showed occlusion of the DAVF (Fig. 1).
3.2. Case report II:Cavernous DAVF (IPS) (Fig.2)
A 54-year-old man presented with blepharoptosis, diplopia and chemosis for 2 months. Cerebral angiograms were obtained and showed a DAVF principally fed by the left meningohypophyseal trunk with additional small branches of the right ICA. Venous outflow empted into the left inferior petroal sinus (IPS) and the left superior ophthalmic vein (SOV). Recommendation was made for transvenous embolization of this lesion. Under general anesthesia, catheterization was performed via transfemoral approach using standard coaxial techniques. Systemic heparinization was achieved during the procedures with heparin 3000U bolus followed by 1000U of heparin every hour. A 5-French diagnostic catheter with continuous heparized flush was positioned in the left ICA for selective control angiograms. The late venous phase of the left ICA angiogram revealed the IPS on this side. Therefore, this IPS was chosen for endovascular approach. A 5-F guiding catheter was placed and, using road mapping technique and fluoroscopic guidance, a microcatheter (Echelon14, MTI-EV3, Irvine, CA, USA) was advanced over a guidwire (Transend0.014, Boston Scientific) into the left IPS up to the left cavernous sinus (CS). Three hydrocoils (two 5×12, one 6×15; MicroPlex) were packed first to reduce the venous outflow towards the SOV. Then, under biplane roadmapping, the catheter was slowly flushed with 0.25ml of DMSO over 40 seconds and this was followed by injection of Onyx (MTI-EV3, Irvine, CA, USA). After 2.3ml of Onyx-34 was injected into the cavernous sinus, we attempted to inject Onyx-18. In the meantime caution was exerted to avoid inadvertent embolization of the left ICA during the slow injection of Onyx. Patency of the left ICA was checked frequently during the intermittent injection of the embolic material. The amount of injected Onyx-18 was 2.6ml. The procedure was completed as soon as a control angiogram revealed complete occlusion of the DAVF. The patient′s chemosis improved within the next day, but blepharotosis and diplopia were not improved. The patient was discharged on the postprocedure day 3.
3.3. Case report III :Cavernous DAVF (Cross-over approach via IPS) (Fig.3)
A 44-year-old woman demonstrated right proptosis and VIth cranial nerve palsy and excessive pulsatile bruits. Cerebral angiography revealed a DAVF of the right CS.Angiography of the right CCA demonstrated persistent filling of the left IPS (Figure 1A). Therefore, a transvenous approach was chosen. The microcatheter was navigated through the left IPS and the intercavernous sinus to the right CS (Figure 1C).The right CS was occluded with 28 standard coils (Figure 1D, E). However, the pulsatile tinnitus was still persistent at six-month follow-up study. Control angiography demonstrated recurrence of the fistula (Figure 1F) and the same procedure was performed (Figure 1G). The residual fistula was occluded completely by another six standard coils (Figure 1H).
3.4. Case report IV:Cavernous DAVF (FV-SOV) (Fig.4)
A 36-year-old female was referred to our hospital again after incomplete transarterial embolization of a cavernous DAVF. On admission, she suffered from slight exophthalmos and chemosis of her right eye. A cerebral angiogram demonstrated a residual arteriovenous shunt of the right CS supplied by the right meningohypophyseal trunk draining to the right SOV. The right facial vein and the right superficial temporal vein were demonstrated angiographically draining the fistula. Because the approach of superficial temporal vein was longer and tortuous, we decided to approach the right CS through the right facial vein. A 5-French guiding catheter (Envoy; Cordis Endovascular System) was advanced through the right internal jugular vein into the right common trunk of facial and retromandibular veins. A diagnostic catheter was placed in the right ICA via the left common femoral artery. A Marathon microcatheter was advanced through the guiding catheter and through the right facial vein into the right SOV. After traversing the SOV, we gain access to the right CS. Occlusion of the fistula was accomplished by filling the right CS with 1.5ml Onyx-34. In the meantime caution was exerted to avoid inadvertent embolization of the ICA during the slow injection of Onyx. Patency of the right ICA was checked frequently during the intermittent injection of the embolic material. There were no complications during the procedure. She was discharged 3 days after the procedure with symptoms improved.
3.5. Case report V:Cavernous DAVF (Direct puncture of SOV) (Fig.5)
A 43-year-old woman had a 2 month history of intracranial bruits, proptosis and chemosis of the right eye. Her vision was normal. An angiogram revealed a CS DAVF draining anteriorly into the enlarged right SOV. The ﬁstula was fed by the meningeal branches of the right ECA and ICA, making it a Barrow type D DAVF. Because of progressive ocular symptoms and intracranial bruits, transvenous embolization was indicated. No IPS was opaciﬁed from either side, and cannulation of either IPS or the facial vein was not successful. Therefore, we recommended surgical exposure and direct cannulation of the right SOV, which was performed in the angiographic suite, as detailed above. A microcatheter was introduced through the trocar sheath, and several platinum coils were deployed into the CS to reduce the ﬂow volume of the ﬁstula. Then, Onyx was used to obliterate the CS until there was no ﬁlling of the CS. Final follow-up angiograms showed complete obliteration of the ﬁstula. Postoperatively, her vision remained normal and the proptosis and chemosis improved within 5 days, and the patient’s intracranial bruits also resolved. A 3 month follow-up angiogram showed durable complete occlusion of the CSDF. The eyelid incision healed well with excellent cosmesis.
3.6. Case report VI:Transverse sigmoid sinus DAVF (Fig.7)
A 56-year-old man with headaches and pulsitile tinnitus demonstrated a left TSS Cognard Type IIa DAVF (Table1). An ophthalmological examination revealed bilateral papilledema. Cerebral angiography demonstrated multiple feeders arising from the left ECA and ICA and basal artery system with a parallel venous channel. One transarterial and one transvenous embolization of the TSS DAVF were performed. These procedures and occlusion of the ECA feeders significantly reduced the size of the fistula. After transvenous embolization of the left TSS, control angiography demonstrated obliteration of the parallel channel, with preservation of the patent parent sinus (Cognard Type I). During the subsequent months the patient′s tinnitus was in stable condition and no further neurological symptoms were noted, ophthalmological examination was not available.
|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
3.7. Case report VII:Tentorial DAVF (Fig.8)
A 70-year-old man presented with a headache of sudden onset and vomiting. Computed tomography demonstrated diffuse subarachnoid hemorrhage and a venous aneurysm at the right petrous apex. Selective right ECA and ICA angiography revealed a dural fistula supplied by branches of the right middle meningeal artery, ascending pharyngeal artery and tentorial branches of the right ICA. The fistula drained in the region of the right petrosal venous complex and thence into the basal vein to the straight sinus. There was a venous aneurysm appropriately 1 cm in diameter on the basal vein. We initially attempted ECA embolization. A microcatheter was placed in the posterior branch of the right middle meningeal artery and embolizing with 5-0 (1.0-1.5cm long) sutures. The ECA suppliers were occluded. But the fistula was still persistent and fed by the branches of the right asending pharyngeal artery and right ICA. We therefore decided on endovascular treatment using a transvenous approach. A microcatheter was placed in the right jugular vein was catheterized and a microcatheter was directed through the straight sinus into the basal vein. The venous varix was crossed with care and the tip of the microcatheter was placed at the site of the fistula in the petrosal venous complex. Using the venous catheter, five EDCs were then placed at the site of the fistula via the transvenous microcatheter. Angiography revealed complete occlusion of the fistula on both the ECA and ICA injections. The patient made an uneventful recovery. After 4 months, the follow-up angiograms of bilateral CCAs confirmed the complete obliteration and the patient demonstrated no symptoms.
Depending on their venous drainage patterns, intracranial DAVFs can cause headaches, dementia, chemosis, proptosis, bruit, and, rarely, infarction or hemorrhage. The data of our patients confirmed previous studies. [3, 6, 11, 37, 45, 51, 52] The clinical presentation is closely related to the degree of shunting, cerebral venous hypertension, and the pattern of venous drainage, with or without impaired cortical function.  Despite spontaneous remission, which occurs in 9.4 to 50% of cases, according to the literature,  treatment is indicated in cases with cortical drainage (Cognard Type IIb or greater), hemorrhage, progressive neurological deficits, or intractable headaches or tinnitus. Although cure rate of DAVFs of transarterial embolization has been promoted by Onyx, it is limited in smaller arteriovenous fistula DAVFs.  Transvenous embolization is still a good option for DAVFs with multiple feeding arteries, especially for transarterial embolization cannot be cured. [17-19] When transvenous catheterization is possible, transvenous embolization is associated with a high rate of permanent long-term occlusion. Occlusion can be achieved with placement of coils, via a transvenous route. Isobutyl-2-cyanoacrylate embolization, particles of polyvinyl alcohol or a detachable balloon have been used to pack the cavernous sinus before advancement of GDC.
5. Transvenous embolization of CS
There are different transvenous route to the CS, i.e., by way of the IPS, contralateral IPS, basilar plexus, or circular sinus, through the facial vein, angular vein, and SOV, or through the pterygoid plexus. [10, 12-14, 17, 23-28, 32, 50-54] To achieve complete occlusion, the cavernous sinus was tightly packed with GDC. This tight packing may have accounted for the intense nausea and vomiting. Transient VIth or IIIrd nerve palsy following coil embolization for cavernous DAVF are well-known events.  The complex nature of the fistula, the unexpected hardship in the placement of detachable coils, and our previous experience with Onyx in the treatment of DAVFs promoted us to use Onyx in the treatment of our patient. [11, 17, 18]
6. Transvenous embolization of DAVFs in other locations
For DAVFs in the ACF, we prefer transvenous procedure with softest EDC and free coils to fit the draining frontal veins and to minimize the risk of damage and rupture of the frontal veins, appreciating the risk of visual compromise from embolic occlusion of the central retinal artery. Although venous approach through the elongated, ectactic, and potentially fragile pial veins is considered difficult and risky, several cases of tentorial DAVF have been treated by transvenous embolization. [14, 19, 21]
If the affected TSS is isolated or exhibits prominent retrograde drainage to the cortical veins and is not a functional part of the venous circulation, then sinus occlusion via an endovascular. If there was anterograde flow in the vein of Labbe in a case of a lateral sinus fistula, the vein of Labbe should be spared after transvenous embolization of the TSS.
Kubo et al.  concluded, on the basis of their three cases and a review of the literature, that second fistulae can occur after complete embolization, with latency periods of more than one year and this finding was confirmed by Kiyosue et al.  For this reason, we occluded all main feeding arteries prior to obliteration of the affected sinus in our cases with DAVFs of tentorium and TSS to prevent development of cortical venous reflux and intracranial hemorrhage. In one patient with a TSS DAVF with a parallel venous channel of the transverse/sigmoid sinus was converted a Cognard Type IIa DAVF into a Cognard Type I DAVF with patent parent sinus.
Transvenous treatment of intracranial DAVFs can be a highly effective method if various transvenous approaches are attempted. Onyx is a promising embolic agent for the transvenous treatment of DAVFs, and its physical properties warrant further appraisal in larger series of patients. The advantages make this an attractive alternative to already described various platinum coils.