Tentorial and Posterior Fossa Dural Arteriovenous Fistulas

Tyler S. Cole, Martin J. Rutkowski, Peter Nakaji, and Michael T. Lawton

Keywords: dural arteriovenous fistula, endovascular embolization, hemorrhage, rupture, microsurgery

33.1 Introduction

Dural arteriovenous fistulas (DAVFs) represent abnormal junctions between arteries and veins or venous sinuses within the dural leaflets. Aberrant hemodynamics make DAVFs susceptible to hemorrhage, often with an annual rupture risk that is three to five times greater than that of brain arteriovenous malformations (AVMs); however, the incidence is one-tenth that of AVMs. These lesions are believed to be acquired, not congenital, with a pathogenesis that is increasingly understood. They can be treated safely and effectively with endovascular, microsurgical, and combined techniques. However, they require a keen diagnostic sense to plan optimal interventions. The majority of DAVFs can be managed and cured through an endovascular approach; nonetheless, posterior fossa and tentorial DAVFs tend to be high-risk for hemorrhage and often fail endovascular embolization, or they are not amenable to endovascular therapy due to anatomical constraints. Although headache and tinnitus are common presentations, in the posterior fossa the variety of presenting symptoms can be wide and includes double vision, visual obscuration, and balance issues or other focal neurologic deficits related to cranial nerve, brainstem, and cerebellar involvement. ^{1,​ 2,​ 3,​ 4,​ 5,​ 6,​ 7} DAVFs located in the cortical venous drainage or in the posterior fossa are independent predictors of hemorrhage. DAVF should be suspected in patients with nontraumatic intracranial hemorrhage with a subarachnoid component. ⁷

33.2 DAVF Classification, Natural History, and Indications for Treatment

The Borden classification is one of several DAVF classification systems that have been proposed. The Borden classification is the most clinically useful system and unifies and simplifies the other classification systems; it has become the accepted classification system. ⁸ Type I DAVFs drain in an anterograde direction into the associated dural venous sinus or meningeal veins. They almost never hemorrhage or produce neurologic deficits, and they are treated only if they become symptomatic. A small number can evolve into type II or III lesions so imaging surveillance may be indicated. Type I DAVFs are treated with transarterial embolization or surgical skeletonization of the venous sinuses if venous drainage needs to be preserved.

Type II DAVFs similarly not only drain into dural venous sinuses or meningeal veins but also drain in a retrograde direction into cortical veins. Type III DAVFs drain exclusively into cortical veins, without venous sinus or meningeal venous drainage. Borden types II and III DAVFs are associated with a risk of hemorrhage and progressive neurologic deficits. Treatment is indicated in patients with these types of DAVFs. Risk factors for hemorrhage include cortical venous drainage, posterior fossa location, and history of hemorrhage. ^{7,​ 9} Type II DAVFs are treated by interruption of the arterialized draining cortical vein and occlusion or excision of the venous sinus. Type III DAVFs can be treated by disruption of the arterialized draining cortical vein.

Resection of DAVFs is not required as with brain AVMs. The draining vein may be occluded using an endovascular method, without resecting the dura containing the DAVF.

33.3 Tentorial DAVFs

Tentorial DAVFs are rare and dangerous lesions. ^{8,​ 10,​ 11,​ 12,​ 13,​ 14,​ 15} A meta-analysis of patients (n = 377) with tentorial, transverse-sigmoid, and cavernous DAVFs showed that patients with tentorial DAVFs had the highest hemorrhage rate or clinical neurologic decline (31/32, 97%). ¹⁰ Tentorial DAVFs are challenging to treat with endovascular therapy and should be decisively treated. ¹³ They have an extensive arterial supply that involves the meningeal arteries from the internal carotid artery and vertebral artery, which are more difficult to embolize and carry greater risk than DAVFs supplied by the external carotid artery. Additionally, tentorial DAVFs frequently drain into subarachnoid veins instead of to their associated sinus (Borden type III), which precludes a transvenous approach. ⁸ Therefore, the management of tentorial DAVFs typically requires microsurgical intervention, in contrast to most other DAVFs. ^{12,​ 16,​ 17,​ 18,​ 19,​ 20,​ 21,​ 22}

Tentorial DAVFs may be categorized into six types, based on anatomical location, dural base, related venous sinus, and type of venous drainage ( ▶ Fig. 33.1). Type I galenic DAVFs may be found in the midline at the posterior border of the tentorial incisura and in association with the vein of Galen as it enters the anterior falcotentorial junction. They may have either supratentorial or infratentorial drainage or both ( ▶ Fig. 33.2). Type II DAVFs are located in the midline along the falcotentorial junction. They are associated with the straight sinus and drain into veins on the undersurface of the tentorium. Type III DAVFs are located in the midline at the posterior border of the falcotentorial junction, and they are associated with the torcula and have supratentorial venous drainage. Type IV DAVFs may be found in the body of the tentorium in association with the tentorial sinus and drain supratentorially into the occipital veins. Type V DAVFs are located laterally where the tentorium joins the dura of the middle cranial fossa. They are associated with the superior petrosal sinus and drain infratentorially into the petrosal vein and its tributaries. Type VI incisural DAVFs may be found along the free edge of the tentorium and are not associated with a venous sinus. They drain into the supratentorial veins in and around the ambient cistern.

33.3.1 Galenic DAVFs

Of the six types of tentorial DAVFs, the galenic type tends to be the most difficult to address. The area around the vein of Galen is particularly deep, and the natural barriers where the falx and tentorium meet can be awkward to navigate. There is no typical direction of arterial inflow. Furthermore, the dilated, tortuous venous architecture often makes the fistulous outflow hard to determine. The combination of surgical depth and complex inflow and outflow necessitates a wide, panoramic exposure that only a torcular craniotomy with an interhemispheric approach can provide ( ▶ Fig. 33.3, ▶ Fig. 33.4, Video 33.1). ²³ With the patient positioned laterally, this approach provides excellent exposure of the torcula, bilateral transverse sinuses, and superior sagittal sinus. After exposing and entering the dura, a wide interhemispheric split is obtained by gravity retraction of the lower occipital lobe, without the use of a retractor ( ▶ Fig. 33.4). Skeletonizing the straight sinus by cutting the falx superior to the straight sinus and the tentorium bilateral to the straight sinus allows views on both sides of the falx and the tentorium. The ambient and quadrigeminal cisterns are readily viewed. If the surgeon prefers, the patient may be positioned for a supracerebellar-infratentorial approach to these lesions. The main advantage of this approach is that, in the case of fistulas that drain inferiorly to cerebellar veins, the surgeon is positioned on the appropriate side of the tentorium for excellent venous exposure. Tentorial incisions can then be made to expose the relevant anatomy more superiorly. The surgeon should consider that the steep slope of the tentorium medially near the vein of Galen can potentially limit the view of critical structures, particularly when the venous anatomy is dilated and tortuous.

Another benefit of skeletonization is concurrent dearterialization of the lesion as the ECA and tentorial feeders are eliminated laterally and the middle meningeal and falcine feeders are eliminated superiorly. The occipital artery supply is eliminated by the craniotomy and dural exposure. If posterior meningeal artery feeders are present, they can be identified and coagulated during dural exposure. However, the primary goal is accomplished when the venous drainage is obliterated. Exposure and skeletonization is mainly a means to better understand and completely visualize the venous anatomy, with the benefit of arterial occlusion.

After careful and delicate dissection of the outflow veins from the fistula, clipping or coagulation of the veins is then performed. The internal cerebral veins are prominent in the posterior view provided by a torcular interhemispheric approach; however, they are rarely the target of occlusion. More commonly, the precentral cerebellar vein and the basal vein of Rosenthal are the targets of occlusion, but they tend to be difficult to occlude. When identifying the basal vein of Rosenthal, a lateral and inferior trajectory can be taken into the ambient cistern. The precentral cerebellar vein is typically located out of view in the surgical corridor inferior to the junction of the falx and tentorium, which after skeletonization can be mobilized easily to identify the cerebellar veins. If an identified vein has a red color and dilated morphology, this appearance indicates fistulous drainage. Blue-colored veins rarely drain pathologic regions. Visual inspection of the vascular anatomy intraoperatively does not always reveal an obvious relationship between the fistula-containing dura and the venous outflow that has been arterialized.

The patency of the straight sinus should be determined by preoperative angiography, as this influences venous occlusion. Most often, galenic DAVFs tend to be Borden type III, draining in a retrograde direction into the vein of Galen or its smaller branches. If the straight sinus is occluded, a clip can be placed directly on the galenic trunk to address the fistulous outflow. The dissection involved in this situation is not extensive and is anatomically straightforward. However, not all straight sinuses are obstructed in these patients. Occasionally, on the venous phase of angiography, antegrade flow is observed in the straight sinus. If this is the case, the patent vein of Galen should be preserved, with care taken to clip or coagulate only the tributary branches of the vein of Galen without interrupting its trunk. If the galenic tributary veins are clearly blue and nonarterialized, these veins may be left to continue draining the deep cerebral circulation to maintain antegrade outflow from normal tissue. (Treatment of galenic DAVFs is discussed in greater detail in Chapter 26.)

Related posts:

How to Repair the Intracranial Aneurysm: Clipping or Coiling Decision Making Distal Anterior Cerebral Artery Aneurysms: Anterior Interhemispheric Approach Middle Cerebral Artery Aneurysms Superficial Cavernous Malformations Superficial Temporal Artery to Middle Cerebral Artery Bypass Transsylvian Transclinoidal and Transcavernous Approach for Basilar Bifurcation Aneurysms

Stay updated, free articles. Join our Telegram channel

Join