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

10.2.2 Treatment Plan

Treatment options were discussed and the patient elected to proceed with transvenous obliteration of the fistulas.

A lateral angiogram obtained with a transvenous microcath-eter positioned within the superior petrosal sinus demonstrated cortical venous reflux. Treatment proceeded with embolization via the superior petrosal sinus to eliminate this reflux. After embolization of the superior petrosal sinus, fistulous connections still existed draining into the transverse sigmoid junction. After coiled embolization of the transverse sigmoid junction, the dAVF was obliterated.

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?

   
   

   There are no set guidelines for follow up for dAVFs. There are few reports citing angiographic change in these lesions to a higher angiographic grade. Partially treated lesions can recruit new feeders and change over time. Even after complete angiographic cure, these lesions can recur. In our practice, we perform diagnostic cerebral angiography on treated dAVFs 12 to 18 months after treatment.

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.

Borden et al proposed a classification that unified spinal and cranial dural arteriovenous fistulous malformations (AVFMs) and organized them in three main types that could provide a rationale for treatment. The authors associated each type with higher or lesser risk of hemorrhage and neurological deficits based upon the pattern of venous drainage and direction and intensity of flow. ⁵ Type I fistulas drained directly into dural sinuses or meningeal veins in an anterograde direction and are often asymptomatic but can present with cranial nerve deficits or pulsatile tinnitus when cranial, or with myelopathy, bruits, and epidural hematomas when spinal. Type II lesions also drained into the dural sinuses, but the arterialized blood flow reversed (retrograde) into the subarachnoid veins, usually presenting with neurological deficits or hemorrhage secondary to venous hypertension. Type III lesions drained directly into the subarachnoid veins or indirectly to it, when the fistula occurs through a segment of dural sinus that is thrombosed on both sides, creating an isolated compartment. Type III fistulas frequently presented with hemorrhage or neurological sequelae secondary to superficial or deep venous hypertension. Subtypes of each dAVFs are also described by Borden in this same study. Treatment is discussed for each type. However, this study was published prior to the significant increase in sophistication of endovascular treatments. Regardless, this study forms the basis for our understanding of dAVFs.

Cognard C, Gobin YP, Pierot L, et al. Cerebral dural arteriovenous fistulas: clinical and angiographic correlation with a revised classification of venous drainage. Radiology 1995;194(3):671-680. ⁶

Cognard et al reviewed 258 patients with dAVFs from their institution. Two hundred and five patients had enough clinical and angiographic data and 120 had follow-up information (mean time = 52 months). The purpose of this study was to correlate the progression associated with each kind of venous pattern seen on angiography. The authors chose to base their observation in the classification proposed by Djindjian but expanded it to five types as seen in ▶ Table 10.1.

Type I dAVFs almost never progressed to more severe types and did not require aggressive treatment attempts. Type Ha lesions could be treated with arterial embolization with particles and, when necessary, with glue and transvenous occlusion in certain locations. Types lib and II a + b have a high risk of bleeding. Occlusion was mandatory in these high-grade lesions and could be done by arterial embolization, transvenous occlusion, or surgical resection of the sinus. Types III to V are very aggressive lesions with a high risk of hemorrhage, which does not change with partial obliteration, requiring therapies such as complete endovascular occlusion, radiosurgery, surgery, or combination of these.

Cognard C, Januel AC, Silva NA }r, Tall P. Endovascular treatment of intracranial dural arteriovenous fistulas with cortical venous drainage: new management using Onyx. AJNR Am J Neu-roradiol2008;29(2):235-241. Epub 2007 Nov 7.

Cognard et al presented a novel use for the new liquid embolic agent Onyx. Thirty patients were prospectively included from 2003 to 2006 to undergo embolization of dAVFs. Ten patients were type II, 8 were type III, and 12 were type IV Of the 25 patients who had never been embolized previously, cure was achieved in 23. Only one patient of the five who had been previously embolized achieved cure. Obliteration was confirmed with follow-up angiography. Of the six patients who achieved partial occlusion, two were successfully cured with surgery and two more with radiosurgery. One cured patient rebled 2 days after embolization, secondary to thrombosis of a draining vein. One patient had transient cranial nerve palsy. The authors considered Onyx a reasonable alternative for treatment of dAVFs and suggested a reconsideration of the global treatment strategies for these fistulas.

Davies MA, TerBrugge K, Willinsky R, Coyne T, Saleh J, Wallace MC. The validity of classification for the clinical presentation of intracranial dural arteriovenous fistulas. J Neurosurg 2 996;85(5): 830-837?

This study is a very interesting analysis demonstrating the reliability of both Borden and Cognard classifications in predicting the presenting behavior of dAVFs. Ninety-eight patients were assessed at a single institution. Hemorrhage and nonhe-morrhagic neurological deficits were considered to be an aggressive presentation. When analyzed according to the Borden classification, aggressive presentation was present in 2% of type I, 39% of type II, and 79% of type III (p < 0.0001) dAVFs. When the Cognard classification was used, aggressive presentation was seen in 0% of type I, 7% of type Ila, 38% of type lib, 40%

of type Ila + b, 69% of type III, 83% of type IV, and 100% of type V lesions (p < 0.0001).