10 Dural Arteriovenous Fistulas
Abstract
The contemporary management of dural arteriovenous fistulas relies heavily on endovascular therapy. Excellent understanding of the clinical manifestations, natural history, and therapeutic approaches is fundamental to obtain the best results. The current endovascular armamentarium allows for a personalized approach to treat the fistulas using the arterial or venous routes, but it remains important to recognize specific circumstances where surgical approaches remain safer and quite effective. While the rarity and the heterogeneity of these lesions remain problematic, a review of the literature allows one to obtain a good grasp to optimize management.
Keywords: dural arteriovenous fistula, endovascular, embolization, management, Borden, Cognard
10.1 Goals
1. Review the literature of dural arteriovenous fistulas (dAVFs) and explain the importance of the angioarchitecture pattern on the natural history.
2. Review the endovascular strategies available to treat dAVFs.
3. Review the roles of the other treatment modalities available for the treatment of dAVFs.
10.2 Case Example
10.2.1 History of Present Illness
A 61-year-old female is seen in consultation in the context of right retroauricular pain with pulsatile tinnitus for approximately 6 months. The patient spontaneously mentioned that manual compression behind her right ear decreased the intensity of the bruit. The patient was initially assessed by an ENT who referred the patient for suspicion of a dAVF. The patient had a recent computed tomography (CT) head and magnetic resonance imaging (MRI) brain without contrast which was negative for any significant pathology.
The patient denied any significant neurological complaints.
Past medical history: Hyperlipidemia, hypertension, gastroesophageal reflux disease (GERD).
No significant history of trauma.
No past medical/surgical ENT or neurological history.
Neurological examination: Unremarkable.
Imaging studies: See ▶ Fig. 10.1 and ▶ Fig. 10.2.
10.2.2 Treatment Plan
Treatment options were discussed and the patient elected to proceed with transvenous obliteration of the fistulas.
Fig. 10.1Cerebral angiogram anteroposterior (AP) and lateral images. Lateral (a) and AP oblique (b) views of external carotid artery injections showing dural arteriovenous fistula (dAVF) feeders from posterior meningeal artery and occipital feeders. Multiple venous tributaries to transverse-sigmoid sinus junction with prominent cortical venous reflux can be visualized.
Fig. 10.2 Endovascular procedure steps: microcatheter in place via transvenous approach (a), initial coils placed showing that there is still filling of the sinus (b), and final result after completion of embolization (c).
10.2.3 Follow-up
The patient did very well after the treatment. The final angiographic run after treatment confirmed complete obliteration. The tinnitus resolved after treatment.
A follow-up angiogram 18 months later confirmed no recurrence or residual shunting.
10.3 Case Summary
1. This patient was found to have a symptomatic unruptured dAVF. No clear abnormalities were documented on CT and MRI. Does negative noninvasive imaging rule out the diagnosis of dAVF?
Catheter-based digital subtraction angiography (DSA) is the mainstay of diagnosis for dAVFs. A six-vessel angiography is necessary for these lesions as the feeding vessels can be bilateral, intra- or extra-cranial, and/or arise from the anterior or posterior circulation. The study of the venous phase is of paramount importance. Although MRI, magnetic resonance angiography (MRA), or computed tomography angiography (CTA) can give valuable diagnostic information, a negative CT or MRI does not exclude the diagnosis of a dAVF. Noninvasive modalities can be helpful adjuncts to DSA, such as detecting hydrocephalus or white matter edema. Also, noninvasive modalities can be the first imaging modality suspecting the presence of a dAVF with detection of prominent pial vessels or tortuous, enlarged veins.
2. What is the expected natural history on this patient?
Patients can present with pulsatile tinnitus, retroauricular pain, intracranial hypertension, venous dementia, seizures, venous infarctions, and intracerebral hemorrhage. Intracerebral hemorrhage is the most dreaded presentation with a case fatality of 20%. The overall risk of annual hemorrhage from dAVF is 1.8%. However, angioarchitecture is the main determinant of the hemorrhage risk. In conservatively managed malformations, 12.5% spontaneously regressed and 4% progressed to higher grade.1 However, the reported spontaneous regression rate for lesions with cortical venous reflux is 3%.2 The two most commonly used classification systems today are Borden and Cognard classification systems. These systems mainly focus on venous drainage patterns and aid in establishing natural history and decision making in treatment. Most Borden type I and Cognard type I and Ha lesions have benign clinical courses, whereas higher grade lesions with cortical venous reflux have higher risks of rupture. In one of the largest series for dAVFs with cortical reflux, the annual rupture rate for untreated lesions was 13%. The same study reported that presence of venous ectasia increased the rupture risk by sevenfold (3.5% no ectasia vs. 27% with ectasia).3
3. Should treatment be considered in this patient?
The decision to treat a dAVF is largely based on the presentation and angioarchitecture (mainly presence of cortical venous drainage). The goal of therapy should be aimed at reducing the risk of rupture or re-rupture. Quality of life improvement can also be a factor in the decision to treat low-risk lesions causing tinnitus. This patient had cortical venous reflux and symptomatic pulsatile tinnitus. The treatment decision was made to eliminate or decrease the annual hemorrhage risk and provide symptomatic relief.
4. If no cortical venous drainage is present, should treatment still be offered?
In patients without cortical venous drainage (Borden I and Cognard 1 and Ila), observation is a viable option. However, treatment may be considered in certain cases. Venous hypertension and related complications such as dementia, hydrocephalus, and intracranial hypertension may necessitate treatment. If possible, complete cure should be the goal of treatment when feasible and safe. However, in selected cases, focused treatments such as addressing a venous sinus stenosis or decreasing overall flow in the lesion by selective arterial embolization can revert the symptoms caused by increased venous pressures. Also, treatment can be considered if symptoms such as pulsatile tinnitus or retroauricular pain are disabling.
5. What treatment alternatives are available to address this entity?
Conservative management, endovascular therapies, open surgery, and radiosurgery are the main options for treatment of these lesions. Asymptomatic or minimally symptomatic lesions without cortical venous reflux can be managed conservatively. Intermittent manual arterial compression could be discussed with limited expectation for asymptomatic/ minimally symptomatic lesions without cortical venous reflux. Endovascular treatment options are currently the mainstay of treatment of dAVFs. Transvenous and transarte-rial routes are the two main options in endovascular management of these lesions. Regardless the route chosen, specific occlusion of the fistulous point with the draining vein offers the best chance for complete cure. Occlusion of only the arterial feeders with intact venous outflow can result in recruitment of new feeders and recurrence of the fistula, though venous occlusion should not be at the expense of normal venous drainage.
Although endovascular therapies should be considered the first-line treatment, open surgery remains a viable option. Currently, the main goal for surgery is to occlude the draining vein when the anatomy allows. Surgery could also be an adjunct to endovascular treatment via accessing the draining vein or sinus for transvenous endovascular treatment. Radiosurgery can also be a viable tool in the armamentarium in the management of dAVFs not amenable to endovascular or surgical treatment. A meta-analysis of the radiosurgical literature reported a rate of obliteration of 63%. Lesions with cortical venous drainage had worse obliteration rate (56%) compared to the ones without (75%).4 Also, it should be kept in mind that radiosurgery has a latency period for dAVF obliteration.
6. Would you follow this lesion after treatment? How would you follow a lesion that is not treated?
10.4 Level of Evidence
Natural history: The natural history of her dAVF with cortical venous reflux is well described through retrospective series (Class I, Level of Evidence C).
Endovascular treatment: The decision to proceed initially with endovascular embolization for a symptomatic, high-grade dAVF is reasonable (Class I, Level of Evidence C).
Follow-up: Angiographic follow-up of treated dAVFs is reasonable, given the recurrence rate of these lesions (Class IIA, Level of Evidence C).
10.5 Landmark Papers
Borden JA, Wu JK, Shucart WA. A proposed classification for spinal and cranial dural arteriovenous fistulous malformations and implications for treatment. J Neurosurg 1995;82(2): 1 66- 179.
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