Dural arteriovenous fistulas (DAVF) of the brain are acquired vascular malformation of the brain. It has low incidence and constitutes to only 10%–15% of all the shunting vascular malformations of the brain. Development of DAVF is secondary to venous sinus occlusion that may be unifocal or multifocal, drainage may be antegrade or retrograde and the clinical presentation is varied based on the location and pattern of venous drainage. Aggressive DAVF has retrograde pattern of venous drainage in the sinuses and drain through cortical veins leading to venous hypertension, cognitive decline and neurological deficit. Rarely, it presents with intracranial haemorrhage. Management of DAVF is predominantly endovascular with open surgical obliteration reserved for few selected cases. DAVF around the trocular herophili remains a challenge as we need to preserve the superficial and deep venous channels for the normal drain drainage. We describe the technical details of flow control and successful obliteration of the torcular DAVF with preservation of sinus.
A 68-year-old patient with a history of computer-aided design presented with progressive lethargy and confusion over the past 1 month. On presentation, her MMSE was 14 and magnetic resonance imaging brain showed multiple abnormal dilated venous channels in both cerebral hemispheres without obvious arterial or venous infarct [Figure 1]. Evaluation with digital subtraction angiography revealed a complex DAVF centered around Torcula herophili and left transveres sinus with complete obliteration of left sigmoid sinus and tight stenosis of the left transverse sigmoid sinus. The feeders to the fistula were from trans bony branches of both occipital arteries, left middle meningeal artery squamous branch, tentorial branches of the meningohypophyseal trunk of the left internal carotid artery, dural branches of the left middle cerebral artery cortical branches, dural branches of the right posterior cerebral artery, posterior meningeal artery and numerous dural branches arising from left vertebral arteries [Figure 1 and Figure 2]. The DAVF had retrograde drainage through the superficial and deep venous sinuses, cortical veins, competing with normal venous drainage of the brain and subsequently draining through the skull base collaterals. There was evidence of significant venous hypertension as evidenced by venous stasis and numerous collateral venous networks [Figure 1f and Figure 1g]. This DAVF was classified as Cognard type IV and Borden Type III.
Goal and therapeutic options
The goal of treatment includes, complete obliteration of all the feeders with preservation of the venous sinuses. Reduction of venous hypertension to achieve cognitive improvement.
The therapeutic option considered here was endovascular embolisation with sinus preservation at the torcular region along with obliteration of left transverse sinus and its feeders. Transarterial embolisation was the primary option and later transvenous balloon was used to achieve flow control and for the preservation of venous sinus patency.
Patient under general anaesthesia, both femoral arteries were accessed and 5 fr short sheaths were placed. Using 5 Fr Envoy catheter, the left occipital artery was catheterised. Using Scepter C Balloon microcatheter over synchro 2 standard wire, the catheter was advanced into the transmastoid branch and Onyx 18 was injected. Good infiltration of the posterior fossa dura was achieved, but as the embolic material entered the vein due to its high flow nature, the embolic material embolised into the vein. Due to retrograde flow patterns in the veins, the emboli flew and lodged at the junction of the straight sinus and accessory falcine venous channel draining towards the Superior sagittal sinus [Figure 3a and Figure 3d]. The embolisation from the right occipital artery was stopped as it was deemed unsafe. Flow control on the venous side was mandatory to achieve safe embolisation of feeders along with preservation of the torcula.
Marathon microcatheter was placed in the left middle meningeal artery distally close to the fistula. The right common femoral vein was accessed, 6 Fr shuttle sheath inserted and placed in the right internal jugular vein. Scepter XC balloon microcatheter was advanced into the left transverse sinus across the torcula. On inflation of the balloon, good flow control was achieved allowing effective embolisation of the feeders from the left middle meningeal artery and surrounding dural arteries with stable filling of the part of the transverse sinus with Onyx [Figure 3]. Again, another marathon catheter was advanced into the right occipital artery and placed distally close to the trans-bony feeders. The venous balloon was placed in the torcular region, inflated to assess the flow. The fistula was not filling and so it was decided to embolise with this location. About 3 ml of Onyx 18 was injected to fill the peritorcular feeders from the occipital artery, posterior meninigeal artery and other dural feeders, posterior cerebral artery, left middle cerebral artery dural branches and tentorial dural arteries. Complete embolisation was achieved with the preservation of the patency of the torcula and all the existing main venous channels [Figure 4]. Control angiogram revealed complete obliteration of the fistula [Figure 5]. The venous pattern of the brain changed with reversal of flow in the superior sagittal sinus, flow across the torcula in antegrade manner and stagnation in the collateral cortical venous channels. The patient was placed on Heparin infusion for 24 h to prevent excess venous clot formation. The patient made a dramatic recovery in the following week to get back to her baseline with an improved MMSE of 28.
DAVF are acquired abnormal arteriovenous connections that develop in the venous sinus wall, its association with sinus thrombosis, surgery, trauma and infection of adjacent Para nasal sinus are all well documented. The abnormality is not a direct arteriovenous shunt but a fine network of connections between dural arteries and veins in the venous sinus wall. Dura is multi-layered fibrous membrane with rich vascular network far excess than its metabolic needs of a membrane while such arterial and venous networks are not present in the pia and arachnoid. The pathophysiological mechanism following the initiating event induces vascular endothelial growth factor (VEGF) production. This along with localised inflammation induces the production of VEGF and other antigenic factors resulting in splitting or sprouting angiogenesis leading to new vascular network formation.
Management of DAVF involves the elimination of the network including the venous channel that in most cases are achieved by endovascular embolisation by either transarterial or transvenous route. In a few selected cases, surgical devascularisation or disconnection of cortical venous drainage is done to achieve cure. Use of stereotactic radiation therapy has reported with an optimal occlusion rate (in approximately 60% of cases) several months after treatment, without significant complications, but it is a long process and considered for only selected cases.
In our case, the dural fistula was located over the walls of the left transverse sinus and torcula herophili. It was important to preserve normal venous drainage of the brain. There was also an associated right transverse sigmoid sinus junction stenosis. The venous drainage of the fistula was retrograde into the superior sagittal sinus, straight sinus and subsequently into the cortical veins competing with already adjusted and compromised normal brain venous drainage. This led to chronic venous congestion in the brain resulting in progressive clinical symptoms. The venous flow was very high in retrograde fashion. Our goal was to achieve complete obliteration of the fistula with preservation of normal venous drainage of the brain including torcula, straight sinus and right transverse sigmoid sinus.
Our first attempt at embolisation through the left occipital artery resulted in good infiltration of onyx in the suboccipital dural network but as onyx reached the vein, it embolised due to high flow into the deep venous system without any clinically significant occlusion. It was decided to have venous flow control to achieve controlled obliteration of the left transverse sinus. The flow control was achieved using temporary balloon obliteration of the transverse sinus using Scepter XC balloon while embolising through the left middle meningeal artery. Good obliteration of the left transverse sinus and its fistulae in the wall and control of cortical venous drainage was achieved. The peri torcular fistulae were far too many on the walls of the sinus all around the venous channel. Despite the retrograde flow, as it is the junction of the superior sagittal sinus and straight sinus our goal was to preserve the torcular patency. We inflated the balloon in the torcular region of the venous sinus and embolised trans arterially to obliterate the DAVF in the wall of torcula herophili was achieved along with preservation of torcula using an inflated dimethyl sulfoxide (DMSO) compatible balloon.
Choi et al. used a covered stent graft to preserve venous sinus flow in a DAVF involving the dominant transverse sigmoid junction in a patient with hypoplasia of the contralateral venous sinuses and intolerable balloon occlusion test for the ipsilateral venous sinuses. Mere conventional stent placement in the affected sinus and with or without angioplasty resulting in compression of the vessels in the sinus wall to achieve occlusion of the arteriovenous shunt flow haemodynamically is published as well. Important concern during stent-graft placement in the venous sinus is initiation and continuation of antiplatelet therapy. However, this was not an option in the torcula region as it is a confluence of the sinus.
Balloon-assisted successful embolisation of DAVF is documented by multiple authors resulting in the high rate of occlusion of DAVF and the technique is refined with the introduction of Copernic RC venous balloon (Balt). This balloon is a low pressure, compliant, large, long and DMSO compatible to preserve long lengths of the sinus allowing more aggressive embolisation of the fistula using Onyx with preservation of venous sinus. One of the major concerns of transvenous balloon-assisted technique is the pressure changes within the intracranial venous drainage when the balloon is inflated, which might cause intracranial hypertension or venous territory infarctions. In cases of embolization involving a dominant venous sinus, the balloon may be periodically deflated to reduce the risk of venous infarction. Adequate systemic heparinisation should also be considered to minimise the risk of dural sinus thrombosis. Risk of onyx migration to a parallel venous channel is also possible and one has to be aware of it. In the series of Piechowiak et al. they have described the migration of onyx into the proximal vein of Labbé despite the use of venous balloon protection. In our case, we used short, super compliant, DMSO compatible Scepter XC balloon of size 4 mm in width and 11 mm in length to focally occlude to achieve flow control and focally obliterate the torcula. The risk of pressure changes with such focal occlusion is very low and we feel this strategy is safe and effective.
Endovascular embolisation is the mainstay treatment for DAVF. To achieve cure, strategising the approach and extent of obliteration based on anatomy and venous drainage pattern of the brain is essential. Torcular DAVF poses a specific challenge, at it is the confluence of the superficial and deep venous system. Transvenous balloon-assisted embolisation is a safe and effective method to achieve complete obliteration of DAVF with preservation of the venous sinuses.
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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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