60 Dural Arteriovenous Fistulas

10.1055/b-0038-162189

60 Dural Arteriovenous Fistulas

Christophe Cognard

Abstract

Dural arteriovenous fistulas (DAVF) are arteriovenous shunts located within the dura. They are acquired and commonly related to cerebral venous thrombosis, head trauma, neoplasia, or postsurgery. Symptoms are secondary to arterialization of venous drainage (pulsatile tinnitus, intracranial hypertension, venous dementia, seizures, venous infarctions, and intracerebral hemorrhages). Type of venous drainage is the most important angiographic feature because it is the basis for the current classification and correlates with fistula aggressiveness. In type I DAVF, only functional symptoms are present; in type IIa DAVF, functional symptoms and risk of intracranial hypertension or dementia are present; in type IIb, III, IV, and V DAVFs, functional symptoms, risk of intracranial hypertension or dementia, and risk of intracranial hemorrhage and venous infarction are present. Type V DAVF has drainage into the perimedullary veins, with venous hypertension of the conus medullaris and progressive myelopathy. Treatment strategies also depend on the type of venous drainage. In type I DAVF, no treatment is necessarily required, arterial embolization with nonadhesive liquid embolic agents (NALEA) is an option. In type IIa DAVF, a more aggressive treatment aiming at DAVF cure is often required and the sinus should not be occluded if the cortical veins are not arterialized. In type IIb DAVF, the sinus can be occluded by venous approach and coiling or arterial approach through the middle meningeal artery and NALEA. In type III, IV, and V DAVFs, arterial NALEA injection aiming at occluding the origin of the draining vein most often obtain a complete cure of the shunt in one procedure. Treatment strategy must be adapted to the neurological risk. Remember that DAVF is a venous disease and anticoagulants are always used postoperatively to avoid extensive thrombosis.

Introduction

Intracranial dural arteriovenous fistulas (DAVFs) are acquired transdural arteriovenous shunts. They are mostly encountered in adults but may be present in newborns as well. They present with a very wide spectrum of symptoms (pulsatile tinnitus, ocular symptoms, intracranial hypertension, dementia, intracranial hemorrhage [ICH], or myelopathy). Depending on their venous drainage, they can be either benign without any neurological risk or aggressive carrying a very high risk of ICH. Perfect understanding of the angioarchitecture and venous drainage patterns is mandatory to evaluate the individual neurological risk for every patient. Treatment strategy basically depends on clinical presentation, venous drainage, and potential neurological risk.

Major controversies in decision making addressed in this chapter include:

Whether or not treatment is indicated for all DAVFs.
Differential diagnosis between DAVFs, pial arteriovenous fistulas, and arteriovenous malformations.
Role of venous drainage and need of treatment.
Open microsurgery versus endovascular treatment for ruptured and unruptured DAVFs.
Endovascular transarterial versus transvenous approach.

Whether to Treat

The initial classification of Djindjian, Merland, and Theron demonstrated a strong correlation between the type of venous drainage and neurological risks. All their patients with type I DAVFs had benign symptoms ( 1 in algorithm ). Patients with type IIa DAVFs had benign symptoms in 63% of the cases. Focal neurological symptoms, venous infarction, or hemorrhage occurred only in cases with cortical venous drainage (types IIb–V; 2–5 in algorithm ). Risk of hemorrhage was higher in the case with direct cortical drainage and in the case with ectasia on the draining vein. Type V DAVFs (a type III or IV DAVF with associated perimedullary drainage) presented in half of the cases with progressive myelopathy similar to a spinal DAVF ( 6 in algorithm ). This classification can be applied to all intracranial DAVFs whatever their location. The classifications of Cognard and Borden correlate with the angioarchitecture, venous drainage, and neurological behavior aggressiveness. In Cognard′s classification, aggressive clinical presentation was observed in: 0% in type I, 7% in type IIa, 38% in type IIb, 40% in type IIa+b, 69% in type III, 83% in type IV, and 100% of type V DAVFs. In Borden′s classification, aggressive clinical presentation was seen in 2% in type I DAVF, 28% in type II DAVF, and 31% in type III DAVF ( 1 –5 in algorithm ; ▶ Fig. 60.1 ).

**Algorithm 60.1** Decision-making algorithm for dural arteriovenous fistulas.

**Fig. 60.1** Artist′s illustration depicting the four different types of dural arteriovenous fistulas. Type IV dural AV fistulas characteristics include enlarged draining veins and aneurysmal dilations (not observed in the current illustration).

Classification

DAVFs were first classified according to their venous drainage in 1978 by Djindjian, Merland, and Theron, and then consequently modified, into five types.

Cognard et al reviewed a series of 205 consecutive patients in order to correlate aggressive neurological behavior of DAVFs to angiographic patterns. Borden et al proposed a simplified classification for both spinal and cranial DAVFs: type I DAVFs drain into dural sinus or meningeal veins; type II DAVFs drain into dural sinus or meningeal veins but also with retrograde drainage into subarachnoid veins; and type III DAVFs drain directly into subarachnoid veins. Currently, the two most commonly used classifications are those of Cognard and Borden.

Pathophysiology

The most feared clinical presentation is ICH and intracranial hypertension. Kuhner et al have postulated that the mechanism of intracranial hypertension in dural fistula is the increased dural and superior sagittal sinus pressure resulting in a secondary diminution of the cerebrospinal fluid (CSF) absorption. The main factor associated with the arterial reflux into sinuses and which contributes to compromise the cerebral venous drainage is the presence of stenosis or occlusion of the sinus downstream the shunt. Sinus lesions secondary to the initial thrombosis may be spread not only to the parent sinus, but also to others. Furthermore, the shunt by itself, due to the arterialization of sinuses, may induce secondary lesions to the sinus wall. Thus, three main factors are of importance in modifying the cerebral drainage: arterialization of the sinus due to the fistula, sinus lesions due to the initial venous thrombosis, and secondary sinus wall lesions due to the arterial flow. Rapidly progressive dementia could be explained by venous hypertensive encephalopathy ( 2 in algorithm ). Myelopathy is not an uncommon clinical presentation of DAVFs. The pathophysiological mechanism of spinal symptoms is spinal cord venous hypertension. Patients presenting with progressive myelopathy have an extensive, slow flow spinal perimedullary venous drainage descending to the thoracic or lumbar spinal cord. In those cases, magnetic resonance (MR) examination shows swelling and hyperintensity of the conus medullaris with contrast enhancement.

Workup

Clinical Evaluation

Almost all the symptoms of DAVFs are related to the arterializations of the sinus/veins draining the fistulas (▶ Table 60.1 ).

**Table 60.1** Symptoms and risks depending on the draining vein/sinus
Venous drainage	Symptoms and risks
Transverse/sigmoid sinus	Pulsatile tinnitus
Ophthalmic veins	Ocular symptoms
Reflux into superior sagittal or straight sinus	Intracranial hypertension, dementia
Cortical veins	Seizures, focal deficits, venous infarction, hemorrhages
Perimedullary veins	Myelopathy

Pulsatile Tinnitus

Pulsatile tinnitus is the most common symptom of DAVFs. Its intensity is very variable; sometimes it is audible only at night during bed rest (▶ Figs. 60.2 – 60.4 ). It decreases during cervical carotid or occipital artery compression. Patients may also present with headaches and retroauricular pain. Vertigo is frequently encountered. Most type I or II DAVFs of the transverse/sigmoid, torcula, or superior sagittal sinuses present with tinnitus.

**Fig. 60.3** Type IIb dural arteriovenous fistula (DAVF). This is a 64 year-old male patient presenting with severe pulsatile tinnitus. **(a,b)** Anteroposterior (AP) view and lateral view of common carotid artery injection demonstrating the type II DAVF. **(c)** External carotid artery injection showing the extensive cortical venous drainage. The patient underwent endovascular embolization. **(d,e)** Venous approach with sinus coil occlusion was performed obtaining a complete fistula obliteration. **(f–h)** A 3-month follow-up angiogram shows residual shunt with cortical venous drainage present (type III) fed by both occipital arteries, lateral **(f)** and AP **(g)** views, and left posterior auricular artery, AP view **(h)**. The patient underwent further embolization. **(i–k)** Distal catheterization of the left posterior auricular artery and Onyx injection were performed obtaining a complete cure, which was confirmed 3 months later by a control angiogram.

**Fig. 60.4** Type IIb dural arteriovenous fistula (DAVF). This is a 37-year-old female patient presenting with severe subacute right-side headache. **(a)** Lateral view of common carotid artery injection demonstrated a type IIb DAVF of the right transverse sinus. **(b–d)** Distal catheterization of the inferior branch of the right-side middle meningeal artery was performed **(b,c)** allowing injecting of 1.8 mL of Onyx in 23 minutes **(d)**. **(e)** Three-month follow-up angiogram confirmed complete cure of the DAVF.

Ocular symptoms

Ocular symptoms are mostly seen in cavernous sinus DAVFs draining into the superior/inferior ophthalmic veins. They include chemosis (94%), exophthalmos (87%), cranial nerve palsy and diplopia (54%), increased intraocular pressure (60%), and impaired vision (28%).

Dementia

Certain DAVFs can present with progressive dementia (▶ Fig. 60.5 ) or Parkinson-like symptoms. In a series published by Hurst et al, 5/40 patients (12.5%) with DAVF presented with rapidly progressive dementia, all symptoms after complete DAVF embolization. Diffused white mater hyperintensities were observed on magnetic resonance imaging (MRI) on patients with DFAVs and dementia.

**Fig. 60.5** Type III dural arteriovenous fistula (DAVF). This is a 55-year-old male patient presenting with rapidly progressive cognitive dysfunction. Anteroposterior **(a,b)** and lateral **(c,d)** digital subtraction angiography demonstrating a type III DAVF of the vein of Galen. The patient underwent endovascular treatment. **(e)** Distal catheterization of the middle meningeal artery (MMA) was performed; due to very high flow and presence of a direct fistula, a flow control was obtained by placing a Scepter C balloon in the origin of the MMA. **(f,g)** Onyx was injected until complete obliteration of the fistula was achieved. **(h)** Complete cure was obtained at the end of the procedure and at 3-month control angiogram.

Intracranial Hypertension, Intracerebral Hemorrhage, and Venous Infarction

In the series by Cognard et al, 20% of the patients with type IIa DAVFs presented symptoms of intracranial hypertension. Seizures, venous infarctions, hemorrhages only occur in cases of DAVFs with retrograde cortical venous drainage (type IIb–V; ▶ Fig. 60.6 ). Davies et al reported a 20% annual mortality and morbidity rate in type IIb to V DAVFs. DAVFs with cortical venous reflux carry a high risk of morbimortality due to hemorrhagic or nonhemorrhagic events both at presentation and in the disease course. Furthermore, the risk of rebleeding is high in patients who already presented with a hemorrhage. Therefore, urgent and complete cure of those DAVFs is necessary to avoid bleeding or rebleeding ( 1 –5 in algorithm ).