Complications in Endovascular Management of Carotid-Cavernous and Dural Arteriovenous Fistulas

Highlights

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The vast majority of dural arteriovenous fistulas and carotid-cavernous fistulas should be treated with an endovascular-first strategy.
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Major complications include unintended embolic migration, cranial neuropathy, and occlusion of normal venous drainage.
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Most complications can be avoided by understanding the relevant cerebral vascular anatomy before any embolization procedure.

Background

Carotid-cavernous fistulas (CCF) and dural arteriovenous fistulas (dAVF) are abnormal communications between the branches of the internal carotid artery (ICA) or external carotid artery (ECA) and the dural venous structures of the head. They vary in clinical presentation, severity, natural history, and indications for treatment largely on the basis of their neurovascular anatomic features. Regardless of location and type, clinical manifestations are the result of venous hypertension. Furthermore, while open surgical interruption of dAVFs is a primary treatment in certain locations, endovascular embolization has become the mainstay of treatment for the vast majority of CCFs and dAVFs. As such, a thorough knowledge of arterial and venous anatomy is essential for the safe endovascular treatment of these lesions, particularly insofar as the dangerous anastomoses responsible for many complications are not always visible on angiography.

CCFs were classified by Barrow et al. into four types based on arterial supply ( Table 43.1 ). Type A fistulas are high-flow fistulas resulting from a direct connection between the ICA and the cavernous sinus (CS). Types B, C, and D fistulas are all low-flow lesions from dural vessels supplying the wall of the CS and originating from the ICA, ECA, or both, respectively. The presenting symptoms are not always the classic triad of exophthalmos, vision loss, and chemosis, and these lesions are often found to present with orbital bruit or cranial neuropathy as well. In general, Type A fistulas tend to present acutely, with more significant clinical manifestations. Direct fistulas have been reported to account for up to 80% of all CCFs, and they are most frequently the result of craniofacial trauma. Spontaneous direct CCFs can occur in the setting of cavernous ICA aneurysm rupture or connective tissue disease, such as Ehlers-Danlos type IV or pseudoxanthoma elasticum. In 2% to 3% of cases, direct fistulas can present up to several weeks after the initial trauma as severe, potentially life-threatening epistaxis. Indirect fistulas, conversely, tend to be more indolent, and spontaneous resolution is common. Presentation varies with the location of the fistulous point within the CS (discussed below). In both direct and indirect fistulas, intracerebral or subarachnoid hemorrhage is a rare finding (less than 5% of patients) but can occur in patients with cortical venous reflux (CVR). Evidence of large varices of the CS or thrombosis of major venous outflow tracts can also predispose to hemorrhagic presentation, and it should lead to emergent evaluation and treatment of the fistula.

TABLE 43.1

Classification of Carotid-Cavernous and Dural Arteriovenous Fistulas

CAROTID-CAVERNOUS FISTULAS		DURAL ARTERIOVENOUS FISTULA
Barrow Classification		Borden Classification		Cognard Classification
Type	Definition	Type	Definition	Type	Definition
A	Direct ICA to CS, high flow	I	Drainage into sinus with antegrade flow	I	Drainage into sinus with antergrade flow
B	Indirect ICA to CS, low flow	II	Drainage into sinus with retrograde flow and cortical venous reflux (CVR)	IIa	Drainage into sinus with retrograde flow and CVR
C	Indirect ECA to CS, low flow			IIb	Drainage into sinus with retrograde flow and CVR
D	Indirect ICA+ECA to CS, Low flow			IIa+b	Drainage into sinus with retrograde flow anf CVR
		III	Drainage into cortical vein (CVR only)	III	Drainage into cortical vein (CVR only)
				IV	Drainage into cortical vein with venous varix
				V	Drainage into spinal perimedullary veins

Dural arteriovenous fistulas are supplied by the dural branches of the ECA, ICA, and vertebral arteries (VAs). These fistulas are named and classified on the venous drainage location and pattern. The Borden classification divides dAVFs into three categories. Drainage of Type I fistulas is anterograde into a dural sinus, Type II fistulas anterograde into a dural sinus and retrograde into cortical veins, and Type III fistulas exhibit isolated retrograde drainage. The Cognard classification follows a similar pattern, but differentiates Type II into IIa and IIb subtypes such that Type IIa fistulas drain anterograde and retrograde into a sinus/sinuses and Type IIb drain anterograde into the main sinus but with retrograde venous reflux. Cognard also added Type IV to denote ectasia of the cortical draining veins (highest risk of hemorrhage), as well as Type V to denote drainage into the perimedullary venous plexus (which can mimic spinal dAVF presentation, particularly for fistulas located near the foramen magnum). CVR has been shown to confer a 10% annual risk of hemorrhage, and Cognard reported that Type III and Type IV lesions were found to be hemorrhagic at presentation in 40% and 65% of patients, respectively. Nonhemorrhagic presentation is most common for low-grade lesions, and can include pulsatile tinnitus, bruit over the fistulous point, and headaches. Encephalopathy can occur from diffuse venous hypertension, and seizures and focal neurologic deficits can be present depending on location.

In both CCFs and dAVFs the urgency of evaluation depends on the acuity and severity of symptoms at presentation. Initial workup with noninvasive imaging, including noninvasive vascular imaging, may suggest an underlying fistula when evidence of an enlarged CS/superior ophthalmic vein (SOV), proptosis, sinus thrombosis, or diffuse engorgement of cerebral veins is seen. However, the gold standard for diagnosis of a CCF or dAVF remains catheter angiography, and endovascular approaches encompass the overwhelming majority of interventions for these lesions.

Anatomic Insights

Venous Anatomy

The cavernous sinus, first described by Jacobus Winslow in 1734, is a misnomer insofar as it is neither cavernous nor a sinus, as demonstrated by the pioneering work of Dwight Parkinson, who preferred lateral sellar compartment as the more anatomically correct term. The reasoning for this designation is that the CS does not contain true cavernous tissue but instead is a plexiform arrangement of septated, compartmentalized venous channels. Furthermore, it is not a true sinus because it lies between the paired dural layers periosteum of the sphenoid bone (not between the two layers of dura). The CS has a number of venous tributaries and routes of egress, which include the superior and inferior ophthalmic veins (IOV), the sphenoparietal sinus, the pterygoid venous plexus via the foramen ovale, the superior and inferior petrosal sinuses (SPS and IPS), the anterior and posterior intercavernous sinuses (known collectively as the circular sinus), and the clival venous plexus. Anatomic variation is the rule in this region, resulting in substantial symptomatic heterogeneity.

These venous pathways to the CS form the basis for the major transvenous embolization techniques. At our institution, indirect CCFs are generally addressed transvenously, proceeding in a stepwise progression from transfemoral access to the IPS, then transfemoral access via the common facial vein system into the SOV, and finally by transpalpebral exposure for direct SOV puncture ( Fig. 43.1 ). Generally speaking, CCFs with fistulous points located anteriorly in the CS tend to present with more significant proptosis/chemosis due to reversal of flow within the SOV, whereas posteriorly positioned fistulas can present with bilateral or contralateral symptoms. Access via the IPS can be variable, based on embryologic development and position of the fistula, but it avoids the intraocular complications of trans-SOV access to the CS. In the setting of long-standing venous hypertension, dilatation of the SOV can expand the veins of the common facial system, enabling transvenous access through this route, but in the absence of these findings, competent venous valves and tortuous pathways can complicate this approach to the SOV. Regardless of the route chosen, a thorough understanding of CS anatomy is essential to understand the unique properties of a given fistula and the likelihood of success with a given embolization strategy.

Dural AVFs vary in presenting symptoms and severity based on how likely a fistula at a given location is to give rise to CVR. Awad et al. reported that over 60% of all dAVFs in their series and metaanalysis were located at the sigmoid sinus and/or transverse sinus, but only one-fourth of these patients presented with aggressive clinical features. Conversely, dAVFs of the tentorium and anterior cranial fossa (ethmoidal dAVFs) almost always present aggressive features and have high rates of hemorrhagic features due to the near-universal absence of direct sinus drainage of these fistulas. Superior sagittal sinus (SSS) dAVFs have a rate of aggressive presentation between these two extremes but often present with extensive bilateral feeding arteries, and torcular fistulas can be a particularly aggressive variant. Drainage patterns of dAVFs at the foramen magnum (including jugular bulb, marginal sinus, and hypoglossal canal) frequently present with myelopathy due to drainage into the perimedullary spinal venous plexus.

Arterial Anatomy

The relevant arterial microanatomy is complex, but certain common arterial anatomic features warrant particular attention because they can be the source of unintended injury to the brain or cranial nerves. Lasjaunias et al., in their comprehensive study of the vascular anatomy of the head and neck, described three regions that serve as the major source of endogenous ECA-ICA anastomoses: the orbital region (via anastomoses with the ophthalmic artery [OphA]), the petrous-cavernous region (via anastomoses with the ICA), and the upper cervical region (via anastomoses with the VAs).

The relevance of the extracranial-intracranial (EC-IC) anastomoses in the orbital region relates to risk of embolization of the central retinal artery (CRA), which arises as the first or second branch of the second segment of the OphA, resulting in blindness. The OphA can collateralize with the middle meningeal artery (MMA) via the anterior falcine artery and the anterior and posterior ethmoidal arteries, or by the meningo-orbital artery and superficial recurrent meningeal arteries that form anastomoses between the MMA and the lacrimal division of the OphA.

Anastomoses in the cavernous-petrous region can result in distal embolization into the ICA via the inferolateral trunk (ILT), as injury to nearby cranial nerves. The cavernous branches of the MMA anastomose with the superior (tentorial) branch of the ILT, both of which anastomose with the petrous arcade supplying the geniculate ganglion through the fallopian hiatus. The ILT also has connections with the superior recurrent meningeal artery to the MMA as well as to the internal maxillary artery (IMA) via the artery of the foramen rotundum (from the distal IMA) and the accessory meningeal artery (AMA) (passing through the foramen ovale or Vesalius to connect to the proximal IMA). Importantly, the ILT has perineural arterial divisions that supply the Gasserian ganglion as well as the cranial nerves running in the lateral wall of the CS. Anastomosis between the carotid canal branch of the ascending pharyngeal artery (APA) and the ILT is also common.

The upper cervical region harbors several anastomoses that are clinically relevant as well. The occipital artery (OA), being a remnant of the embryologic type I and II proatlantal arteries, still serves as an endogenous connection between the VA and the ECA, sending branches from its horizontal segment to the VA at the level of C1/C2. In some patients this embryologic origin is clearer, with shared origin of the distal OA from both the ECA and VA visible angiographically ( Fig. 43.2 ). The neuromeningeal branches of the APA (jugular and hypoglossal) anastomose with the VA at the artery of the dens, and also form connections with the ILT and meningohypophyseal trunk (MHT) via their clival branches.

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