Key points

Introduction

Dural arteriovenous fistulas (dAVF) represent approximately 15% of all intracranial vascular malformations. Significant gaps remain in the understanding regarding dAVF pathogenesis and treatment. The underlying pathophysiology for the development of intracranial dAVF has been refined with the advancement of several theories, including changes in blood flow dynamics at the site of a pre-existing dural venous thrombosis and increased expression of angiogenic factors, such as vascular-endothelial growth factor (VEGF) in adjacent dural leaflets. However, the lack of venous thrombosis in some dAVF can be used to argue against the need for vascular stasis, whereas the absence of clear causative information regarding increases in local VEGF levels in dural samples casts doubt on the importance of these signaling pathways in the creation of dAVF.

With the recent advances in endovascular and radiosurgical techniques, along with a better understanding of the pathophysiology and clinical course of intracranial dAVF, individualized treatment that is both effective and safe can be offered to most patients with intracranial dAVF. The choice of the best therapeutic strategy should take into account the clinical presentation, location of the dAVF, angioarchitecture, and patient’s preference. Treatment is indicated in patients with disabling symptoms, presence of retrograde cortical venous drainage (CVD), and those with aggressive clinical presentation (hemorrhage or symptoms and signs related to venous hypertension).

Patients with minimal or no symptoms and no evidence of retrograde CVD may be well served with observation alone. In these patients, the dAVF are usually located at the transverse/sigmoid junction and the cavernous sinus. In patients with transverse/sigmoid sinus dAVF and no CVD, the natural history is very benign and such cases have a very low risk of hemorrhage. These patients usually present with symptoms related to the high-flow, low-pressure shunt, such as a bruit or localized pain. Alternately, such patients can be completely asymptomatic. In patients with a bruit, the bruit resolves or improves without treatment in approximately 50% of patients. In these cases, the dAVF often undergoes spontaneous regression and even resolution over time. In the presence of disabling symptoms but no retrograde CVD, use a strategy is often used that combines particle embolization for symptom palliation, and reduces the flow through the fistula followed by stereotactic radiosurgery (SRS). This strategy usually results in symptom resolution and obliteration of the fistula in more than 70% of patients (usually within a year) while preserving the patency of the involved sinus.

The presence of retrograde CVD in patients with dAVF involving a large dural sinus is often associated with progressive neurologic symptoms and disturbance of the venous drainage from the normal brain parenchyma. In these cases, a more aggressive therapy with the goal of rapid angiographic obliteration is required; this is particularly true if the venous drainage is associated with a cortical venous varix, which may increase the risk of hemorrhage. In these cases, a transvenous approach with coil embolization of the involved sinus is preferred, which may be patent but often is not functional because it is used for the drainage of the fistula and hence arterialized.

Indirect cavernous carotid fistulas (CCF) represent a unique type of dAVF. In patients with minimal symptoms, no retrograde CVD, and normal intraocular pressure, SRS with or without transarterial particulate embolization is a safe and effective therapeutic strategy. In patients with indirect CCF and retrograde CVD and/or progressive symptoms or increased intraocular pressure, a more direct and immediate treatment is preferred, which usually involves a transvenous catheterization and occlusion of the involved area with coils and more recently Onyx in combination with coils. In these cases, the venous access to the cavernous sinus may be difficult, in which case a direct percutaneous puncture and access can be used.

Patients who present with hemorrhage also require a treatment that should be immediate and curative. The risk of rebleeding after a first hemorrhagic episode is quite high in patients with dAVF, especially if a venous varix is present along the drainage pathway. Many of the patients who present with hemorrhage have dAVF in locations other than the more common transverse/sigmoid junction or the cavernous sinus. Most the fistulas presenting with hemorrhage are located in the tentorium and the anterior cranial fossa and have exclusive retrograde CVD. Onyx has dramatically improved the ability to treat effectively and safely most of the tentorial dAVF, which only a few years ago were considered almost exclusively “surgical” fistulas. Transarterial Onyx embolization has a much higher chance of being effective if the posterior branch of the middle meningeal artery is one of the main feeders to the dAVF. This branch is relatively straight and allows for distal catheterization, which in turn improves the likelihood of anterograde migration of the embolic agent. For this strategy to be effective, the proximal portion of the draining vein must be completely obliterated.

Although embolization of anterior cranial fossa dAVF is feasible, surgical resection or SRS remain the preferred treatment options because of the risk of blindness from reflux of the embolic material into the ethmoidal branches of the ophthalmic artery. In the presence of aggressive clinical symptoms, surgery is also considered for those dAVF in locations other than anterior cranial fossa if embolization is not feasible or fails to obliterate the fistula completely.

With widespread utilization of axial imaging studies, a large number of dAVF are currently diagnosed in patients with minimal or no symptoms. Some of these incidental fistulas have dangerous angiographic features, including locations prone to hemorrhage (tentorial, anterior cranial fossa), presence of retrograde CVD, or an associated venous varix. In these cases, treatment in younger patients and especially in those with associated venous varices is recommended. Embolization, SRS, or a combination of both techniques is usually the main treatment strategy in these cases. Resection is reserved for those patients who fail embolization and radiosurgery. In the authors’ experience, SRS is very effective in dAVF involving a large dural sinus, such as the transverse/sigmoid, the superior sagittal sinus, and indirect CCF.

Introduction

Dural arteriovenous fistulas (dAVF) represent approximately 15% of all intracranial vascular malformations. Significant gaps remain in the understanding regarding dAVF pathogenesis and treatment. The underlying pathophysiology for the development of intracranial dAVF has been refined with the advancement of several theories, including changes in blood flow dynamics at the site of a pre-existing dural venous thrombosis and increased expression of angiogenic factors, such as vascular-endothelial growth factor (VEGF) in adjacent dural leaflets. However, the lack of venous thrombosis in some dAVF can be used to argue against the need for vascular stasis, whereas the absence of clear causative information regarding increases in local VEGF levels in dural samples casts doubt on the importance of these signaling pathways in the creation of dAVF.

With the recent advances in endovascular and radiosurgical techniques, along with a better understanding of the pathophysiology and clinical course of intracranial dAVF, individualized treatment that is both effective and safe can be offered to most patients with intracranial dAVF. The choice of the best therapeutic strategy should take into account the clinical presentation, location of the dAVF, angioarchitecture, and patient’s preference. Treatment is indicated in patients with disabling symptoms, presence of retrograde cortical venous drainage (CVD), and those with aggressive clinical presentation (hemorrhage or symptoms and signs related to venous hypertension).

Patients with minimal or no symptoms and no evidence of retrograde CVD may be well served with observation alone. In these patients, the dAVF are usually located at the transverse/sigmoid junction and the cavernous sinus. In patients with transverse/sigmoid sinus dAVF and no CVD, the natural history is very benign and such cases have a very low risk of hemorrhage. These patients usually present with symptoms related to the high-flow, low-pressure shunt, such as a bruit or localized pain. Alternately, such patients can be completely asymptomatic. In patients with a bruit, the bruit resolves or improves without treatment in approximately 50% of patients. In these cases, the dAVF often undergoes spontaneous regression and even resolution over time. In the presence of disabling symptoms but no retrograde CVD, use a strategy is often used that combines particle embolization for symptom palliation, and reduces the flow through the fistula followed by stereotactic radiosurgery (SRS). This strategy usually results in symptom resolution and obliteration of the fistula in more than 70% of patients (usually within a year) while preserving the patency of the involved sinus.

The presence of retrograde CVD in patients with dAVF involving a large dural sinus is often associated with progressive neurologic symptoms and disturbance of the venous drainage from the normal brain parenchyma. In these cases, a more aggressive therapy with the goal of rapid angiographic obliteration is required; this is particularly true if the venous drainage is associated with a cortical venous varix, which may increase the risk of hemorrhage. In these cases, a transvenous approach with coil embolization of the involved sinus is preferred, which may be patent but often is not functional because it is used for the drainage of the fistula and hence arterialized.

Indirect cavernous carotid fistulas (CCF) represent a unique type of dAVF. In patients with minimal symptoms, no retrograde CVD, and normal intraocular pressure, SRS with or without transarterial particulate embolization is a safe and effective therapeutic strategy. In patients with indirect CCF and retrograde CVD and/or progressive symptoms or increased intraocular pressure, a more direct and immediate treatment is preferred, which usually involves a transvenous catheterization and occlusion of the involved area with coils and more recently Onyx in combination with coils. In these cases, the venous access to the cavernous sinus may be difficult, in which case a direct percutaneous puncture and access can be used.

Patients who present with hemorrhage also require a treatment that should be immediate and curative. The risk of rebleeding after a first hemorrhagic episode is quite high in patients with dAVF, especially if a venous varix is present along the drainage pathway. Many of the patients who present with hemorrhage have dAVF in locations other than the more common transverse/sigmoid junction or the cavernous sinus. Most the fistulas presenting with hemorrhage are located in the tentorium and the anterior cranial fossa and have exclusive retrograde CVD. Onyx has dramatically improved the ability to treat effectively and safely most of the tentorial dAVF, which only a few years ago were considered almost exclusively “surgical” fistulas. Transarterial Onyx embolization has a much higher chance of being effective if the posterior branch of the middle meningeal artery is one of the main feeders to the dAVF. This branch is relatively straight and allows for distal catheterization, which in turn improves the likelihood of anterograde migration of the embolic agent. For this strategy to be effective, the proximal portion of the draining vein must be completely obliterated.

Although embolization of anterior cranial fossa dAVF is feasible, surgical resection or SRS remain the preferred treatment options because of the risk of blindness from reflux of the embolic material into the ethmoidal branches of the ophthalmic artery. In the presence of aggressive clinical symptoms, surgery is also considered for those dAVF in locations other than anterior cranial fossa if embolization is not feasible or fails to obliterate the fistula completely.

With widespread utilization of axial imaging studies, a large number of dAVF are currently diagnosed in patients with minimal or no symptoms. Some of these incidental fistulas have dangerous angiographic features, including locations prone to hemorrhage (tentorial, anterior cranial fossa), presence of retrograde CVD, or an associated venous varix. In these cases, treatment in younger patients and especially in those with associated venous varices is recommended. Embolization, SRS, or a combination of both techniques is usually the main treatment strategy in these cases. Resection is reserved for those patients who fail embolization and radiosurgery. In the authors’ experience, SRS is very effective in dAVF involving a large dural sinus, such as the transverse/sigmoid, the superior sagittal sinus, and indirect CCF.