Carotid cavernous fistulas (CCFs) are abnormal arteriovenous shunts between the internal carotid artery (ICA) and the cavernous sinus either via direct connection with the ICA and/or its intracavernous branches or via external carotid artery (ECA) branches and the venous channels associated with the cavernous sinus. In keeping with the pathophysiology of most intracranial arteriovenous fistulas, CCFs as well cause symptoms via venous hypertension and exert their effect on surrounding tissue by venous engorgement and mass effect on adjacent structures. The venous drainage pattern therefore becomes an important anatomical feature that determines symptomatology. As such, CCFs can manifest themselves as proptosis and injection of the globe resulting in vision loss from increased intraocular pressure or by compression on cranial nerves passing through the cavernous sinus. Additionally, some may exhibit leptomeningeal retrograde venous drainage via collateral venous drainage between the cavernous sinus and sylvian veins, creating risk for intracranial hemorrhage.

31.2 Patient Selection

31.2.1 Classification

A useful classification for CCFs emphasizes the venous drainage pattern of fistulas and correlates with the clinical behavior observed in natural history studies. ^{1,​ 2} The Borden classification of dural arteriovenous fistulas is only partly applicable to CCFs. In this system, type 1 lesions have drainage only into a dural sinus or meningeal veins, type 2 fistulas drain into a dural sinus and leptomeningeal veins, and type 3 lesions drain into leptomeningeal veins only. Those fistulas with leptomeningeal venous drainage (Borden types 2 and 3) are associated with an aggressive natural history and high incidence of hemorrhage or progressive neurological complications. The risk is high—nearly 20% annually with mortality of about 10% for such fistulas that have a history of hemorrhage. Emerging data suggest that even the Borden 2 and 3 fistulas may have a relatively benign natural history if they are diagnosed in patients with no evidence of a prior hemorrhage. ³

In general, fistulas draining exclusively into a dural sinus (Borden type 1) have a benign natural history. CCFs are one exception to this generalization and they have unique characteristics and are better classified by other systems ( ▶ Fig. 31.1, ▶ Fig. 31.2, ▶ Table 31.1). ¹ By inducing cavernous sinus hypertension, CCFs may lead to orbital venous engorgement that can cause pain, pulsatile exophthalmos, exposure keratopathy, conjunctival chemosis, and ocular motility restriction. These symptoms may progress to retinal ischemia/detachment, glaucoma, and ultimately visual loss.

31.2.2 Indications for Treatment

Treatment decisions are based on the local orbital symptomatology and by the pattern of venous drainage. Noninvasive treatment options such as observation and ipsilateral carotid compression may be appropriate for Borden type 1 lesions without objective ocular impairment or raised intraocular pressure (usually Barrow types B to D). Once leptomeningeal venous drainage, ocular impairment due to venous hypertension (chemosis, exophthalmos, ocular motility restriction, etc.) or orbital venous hypertension is detected, treatment is indicated to prevent hemorrhagic complications or visual loss.

The timing of treatment depends on the presenting features. Urgent treatment is indicated for CCFs with rapidly progressing visual compromise, markedly increased intraocular pressure (> 40 mm Hg) or focal neurological deficits other than cavernous sinus symptoms (usually secondary to leptomeningeal venous hypertension). Because of the high risk of hemorrhage from Borden 2 and 3 lesions, timely treatment of these is also indicated. A rare emergent complication is epistaxis, which can be torrential if there is a fracture or erosion through the thin sphenoid sinus wall.

31.2.3 Treatment Options

The goal of treatment of most fistulas, including CCFs ideally should be to obliterate the arteriovenous shunt at the site of fistula while preserving patency of the cerebral arteries, in this case the ICA. Treatment options include observation, carotid compression, transarterial and/or transvenous embolization, and microsurgical approaches to facilitate embolization or accomplish venous disconnection. Because of the benign course of those CCFs draining exclusively into the cavernous sinus (Borden type 1), such patients can be managed with observation or intermittent carotid compression. Manual carotid compression is done six times a day for 30 seconds each session over a period of 4 to 6 weeks. It is very helpful to demonstrate the technique to the patient with instructions to use the contralateral hand to compress the carotid artery in the neck. If this causes cerebral ischemia, the compressing extremity weakens and the manual pressure stops. The patient should be sitting to prevent a fall resulting from a vasovagal attack. Stop antiplatelet or anticoagulation treatment during this period. To induce thrombosis, the carotid and jugular flows should be compressed together and any bruit should disappear. Close neurological and neuro-ophthalmological follow-up is important. This includes visual acuity, pupillomotor activity, intraocular pressure, visual fields, proptosis measurement, gonioscopy, and direct and indirect fundoscopy. Occasionally spontaneous resolution of benign symptoms, like bruit, is caused by conversion of venous drainage solely into the cavernous sinus to a leptomeningeal route, signifying the transformation of a benign dural arteriovenous malformations (DAVMs) to an aggressive type. On the other hand, resolution of symptoms can also mean resolution of the fistula, which can occur spontaneously or after diagnostic angiography alone.

For patients with neurological or serious ophthalmic dysfunction, or when they harbor Borden type 2 or 3 lesions, aggressive therapy is indicated. We recommend treatment for visual deterioration, diplopia related to vascular engorgement and enlargement of the extraocular musculature or to neural compression within the cavernous sinus, intolerable bruit or headache, and/or severe proptosis with refractory exposure keratopathy. Transvenous embolization is the preferred treatment, although transarterial embolization is a reasonable alternative if all fistulous feeders are from the external carotid system.

Transarterial embolization was previously a major treatment for DAVMs. The cure rates range from 70 to 80%. At present, this option is chosen for lesions with predominant ECA feeders and in which venous embolization is not feasible due to either poor access or high risks. Transarterial closure of direct CCFs with detachable coils with or without the addition of liquid embolic agents is also well described. ^{4,​ 5,​ 6,​ 7} In patients who tolerate balloon test occlusion on the side of the fistula, carotid sacrifice with coil placement both proximal and distal to the site of the fistula can be very effective. Combination of transarterial embolization with stereotactic radiosurgery has been reported.

The transvenous approach has become the treatment of choice for most DAVMs, including CCFs. Difficulty may be encountered from multiple peripheral valves when catheterizing the femoral vein. From the internal jugular vein, the inferior petrosal sinus is the most common access to the cavernous sinus. Occasionally, microguidewires and microcatheters can be maneuvered through a thrombosed inferior petrosal sinus. Many other access routes have been described, including the superior ophthalmic and angular veins, superior petrosal sinus, pterygoid plexus, and dilated cortical draining veins. Direct percutaneous puncture of the SOV and even the cavernous sinus through the superior orbital fissure has also been performed. Detachable coils are typically used for embolization. Complete packing of the cavernous sinus can be tolerated, although some have been successful at preserving the normal sylvian drainage into the sinus while obliterating the fistula.

While transvenous and transarterial access to the cavernous sinus through standard endovascular techniques has yielded excellent results and is probably the first treatment option, on occasion conventional endovascular routes may not be available either as a result of venous stenosis or occlusion, or from surgical carotid occlusion or fistula trapping. In some instances an engorged superior ophthalmic vein (SOV) may be present, allowing direct surgical exposure and access to the cavernous sinus. In the challenging circumstance of a completely trapped CCF without ophthalmic venous outflow, the cavernous sinus can be accessed surgically through a modified pterional craniotomy with pretemporal extradural dissection. A less invasive approach is a percutaneous transorbital, infraocular cavernous sinus puncture via the superior orbital fissure (transorbital puncture).

31.3 Preoperative Preparation

Thorough angiographic investigation is a prerequisite for treatment. Lateral series are the most valuable, although the anteroposterior series of the ipsilateral ICA is performed to show any reflux into cortical veins and across the circular sinus to the opposite side. Contralateral carotid angiograms may help to detect bilateral CCFs, significant stenosis, occlusion, or aneurysm that may complicate possible ipsilateral carotid sacrifice. An ipsilateral vertebral artery injection can establish the level of the fistula, as well as the collateral circulation of the circle of Willis.

31.4 Operative Procedure

31.4.1 Surgical Exposure of the Superior Ophthalmic Vein

A 15-mm incision is made at the medial lid crease or the subbrow region after infiltration of a local anesthetic with epinephrine. Blunt dissection is used to identify the orbital septum ( ▶ Fig. 31.3). Just beneath the superior orbital rim at the level of the trochlea, the orbital septum is incised along the width of the skin incision, with the trochlea and superior oblique tendon identified and protected. The orbital fat is retracted laterally with blunt dissection. In the medial orbit just posterolateral to the trochlea the SOV will appear ( ▶ Fig. 31.3). Frequently, the vein is arterialized and quite fragile. The vein is skeletonized with blunt dissection, and two 2–0 silk ligatures are placed around the vessel for manipulation and retraction. Between the ligatures, venipuncture is performed and a mandrel guidewire (Cook, Bloomington, IN) is introduced, followed by a 4 French micropuncture introducer (Gait Medical Corp., Garland, TX) for SOV catheterization. An additional suture through the periosteum of the arcus marginalis can be used to secure the cannula. A standard 4 French diagnostic catheter is linked to the introducer ( ▶ Fig. 31.3), so that embolization through a microcatheter can be performed with standard endovascular techniques with better ergonomic control and less radiation exposure to the clinicians.

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