Carotid-cavernous fistulas

INTRODUCTION — Acquired rather than congenital vascular malformations, carotid-cavernous fistulas (CCFs) may arise spontaneously or from secondary causes. CCFs can present with a variety of signs and symptoms. Many lesions are associated with significant neuro-ophthalmologic morbidity and mortality. Treatment decisions require multiple considerations: the nature of the symptoms, the location of the lesion, the complexity of the angioarchitecture, and the risk of visual and neurologic morbidity.

This topic discusses the pathogenesis, clinical presentation, diagnosis, and management of CCFs. Other vascular malformations of the central nervous system are discussed separately. (See "Brain arteriovenous malformations" and "Vascular malformations of the central nervous system".)

CLASSIFICATION — CCFs arise from abnormal communications between the carotid arteries and the cavernous sinus.

CCFs may be high- or low-flow lesions:

●High-flow CCFs result from a direct connection between the intracavernous carotid artery and the surrounding cavernous sinus.

●Low-flow CCFs represent a subtype of dural fistula resulting from indirect communication between the cavernous sinus and branches of the internal or external carotid artery within the adjacent dura. These are often referred to as cavernous dural fistulas or dural CCFs.

In the Barrow classification, CCFs are further subdivided into four types based on their etiology, rate of flow, and source of feeder vessels [1]. Type A CCFs are direct, high-flow lesions connecting the carotid artery and cavernous sinus, and they often result from a single, endothelialized tear in the carotid wall [2]. Types B, C, and D fistulas are low-flow, indirect lesions that vary by anatomy. The arterial supply of Type B lesions arises from small branches of the cavernous carotid artery, Type C from dural branches of the external carotid, and Type D from a combination of external and internal carotid artery (ICA) branches. Barrow type B, C, and D fistulas are often referred to as cavernous dural fistulas.

EPIDEMIOLOGY — Estimates of the incidence of CCFs are not documented in the literature. Overall, CCFs are found equally in males and females and can occur in any age group, including young children [3]. Occurring most often as a consequence of traumatic injury, direct CCFs were found in one study to occur in up to 4 percent of patients who had sustained a basilar skull fracture [4]. As with other traumatic injuries, young men are the demographic group most often affected [5-7]. By contrast, dural CCFs (Barrow type B-D) are somewhat more common in older women [8-12].

ETIOLOGY — CCFs may arise spontaneously or from secondary causes, including trauma, cavernous carotid aneurysm, venous thrombosis, and genetic conditions associated with arterial wall defects. In many cases, no cause can be identified.

The majority of direct, type A CCFs result from head trauma [5,6,13]. Symptoms may manifest immediately or be delayed for days or weeks. The trauma is generally severe and is accompanied by skull or facial fractures. Post-traumatic CCFs are bilateral in 1 to 2 percent of patients [4,5].

The exact mechanism by which the CCF results from trauma is uncertain. Hypotheses include a tear in the artery from a bony fracture or shear forces versus a sudden elevation in intraluminal pressure resulting from abrupt compression of the carotid artery during sudden neck flexion [3,14]. Penetrating trauma and iatrogenic injuries may also result in high-flow CCFs. Iatrogenic fistulas have been reported after carotid endarterectomy surgery, endovascular procedures, transsphenoidal pituitary surgery, and sinus surgery [15-18].

Most CCFs that are not associated with trauma are idiopathic [19]. Some high-flow CCFs may arise from rupture of a preexisting cavernous sinus aneurysm [1,5,6,20-22]. In one series of 51 carotid sinus aneurysms, 10 (24 percent) presented with a CCF [21]. By contrast, in another study of 174 patients with cavernous sinus aneurysms, only 13 (7.5 percent) presented with CCF [20]. Eighty-eight patients with unruptured, untreated aneurysms were subsequently followed for a mean of 4.5 years; none of these aneurysms were associated with rupture or CCF formation over this time period.

Genetic conditions associated with spontaneous direct CCFs include fibromuscular dysplasia [19,23,24], Ehlers-Danlos syndrome [25-28], and pseudoxanthoma elasticum [29,30]. It is hypothesized that these patients have a defect in the arterial wall that ruptures from relatively minor trauma such as coughing or Valsalva.

Dural CCFs (Barrow type B-D) may arise from preexisting microscopic communications between dural arteries and venous sinuses [14,31]. Factors that induce venous thrombosis or increase venous pressure are thought to increase the number and size of these microscopic shunt vessels. A hormonal effect was postulated but not proven in a few reported cases of CCF occurring during pregnancy and the postpartum period; however, a relative hypercoagulable state during this period may also have contributed [32-34]. Indirect CCFs may also follow head trauma, but this is less common than with direct, high-flow CCF [13,35]. Hypertension may be another risk factor for spontaneous CCF formation [1,35].

CLINICAL PRESENTATION

High-flow carotid-cavernous fistulas — The characteristic clinical presentation of patients with high-flow direct CCFs results from the arterialization of orbital veins. The onset of symptoms is usually abrupt and may progress rapidly. Common symptoms and signs on presentation include [5-7,13,16,36]:

●Subjective bruit (80 percent), bruits may also be auscultated over the globe

●Blurred vision (25 to 59 percent)

●Headache (53 to 75 percent)

●Diplopia (50 to 85 percent)

●Ocular and/or orbital pain (35 percent)

●Proptosis (72 to 87 percent)

●Chemosis and conjunctival injection (55 to 89 percent)

With respect to ophthalmoplegia, cranial nerve VI is involved in 50 to 85 percent of cases, cranial nerve III is involved in 67 percent of cases, and cranial nerve IV is involved in 49 percent of cases [5,16]. Facial sensory loss may also result from involvement of cranial nerve V. Cranial neuropathies can be difficult to distinguish from deficits acquired from the initial trauma.

Funduscopic examination can reveal nonspecific findings of venous stasis retinopathy with dilated retinal veins and intraretinal hemorrhages (picture 1). These along with proptosis, chemosis, and eyelid swelling can result from vascular congestion (picture 2). If severe, this can lead to exposure keratopathy and sight-threatening corneal ulceration. Arterialization of conjunctival and episcleral vessels results from blood forced into the venous drainage of the orbit. This can result in elevated episcleral venous pressure, secondary glaucoma, and, rarely, catastrophic central retinal artery occlusion [13].

When CCF drains into cortical veins, spontaneous rupture can result in intracerebral or subarachnoid bleed in 5 percent of patients [6,7,14]. Life-threatening epistaxis complicates a minority of direct CCFs [37,38].

Low-flow carotid-cavernous fistulas — Dural or indirect CCFs (Barrow type B-D) are seen most often in woman over the age of 50, and have a less fulminant presentation than do the high-flow CCFs [14]. There is often no objective or subjective bruit [8,9,39]. Involvement of the fifth and seventh cranial nerves is also uncommon with these lesions [40]. Dural CCFs can produce specific patterns of symptoms based on the rate of flow and the pattern(s) of venous drainage [9,11]:

●Anterior-draining dural CCFs are the most common and usually present with ocular and orbital symptoms including chemosis, conjunctival injection, and proptosis due to congestion of the superior ophthalmic vein [9]. Affected individuals are often treated prior to definitive diagnosis with antibiotics or topical steroids for a "red eye." Arterialization of conjunctival vessels has a characteristic corkscrew appearance with an acute angulation near the limbus (picture 3) [41]. There may be significant pain as well. Abducens (cranial nerve VI) palsy is the most common cause of diplopia in these patients. Loss of vision can affect one-third of patients in this category and may result from increased intraocular pressure secondary to orbital venous congestion and glaucoma, venous retinopathy, and ischemic optic neuropathy. Neurologic morbidity is relatively uncommon in this group.

●In patients with dural CCFs that drain posteriorly into the inferior or superior petrosal sinus, orbital symptoms (proptosis, chemosis, lid edema) are often absent; these patients instead present with a "white-eyed" painful diplopia [8,42-45]. The oculomotor nerve (cranial nerve III) is most commonly involved, with or without pupillary involvement. Sixth and fourth nerve palsies are also frequently seen. Concomitant drainage into cortical veins is more common when the dominant drainage is into the superior petrosal sinus [9,46].

●Patients with drainage into cortical veins (eg, sylvian vein, basal vein of Rosenthal) are at risk for venous infarction and intracranial hemorrhage [8,39,47,48]. Patients with cortical drainage may have neurologic symptoms, even in the absence of frank infarction or hemorrhage, possibly related to venous congestion or ischemia from shunting of blood flow [47]. Approximately one-third of patients with dural CCFs have evidence of cortical venous drainage on angiography [10,12,49].

●Bilateral orbital venous drainage of a CCF may lead to bilateral or even contralateral symptoms [9,10,47]. Patients with bilateral orbital venous drainage with a unilateral dural CCF are more likely to also have cortical venous drainage [47]. Alternatively, some patients present with bilateral dural CCFs. In one case series of 85 patients, 25 presented with bilateral symptoms, 10 of whom had documentation of bilateral fistulas [9]. An additional three patients had bilateral fistulas but with symptoms only on one side.

The pattern of venous drainage can change due to the development of thrombosis; as an example, a posteriorly draining CCF may evolve into one that drains mostly anteriorly [8]. Symptoms may also wax and wane as the result of spontaneous thrombosis and subsequent clot dissolution.

Vision loss is more problematic in the setting of anterior drainage and prominent orbital signs and can affect one-third of patients in this category [9,10,44,50-53]. Causes of vision loss include:

●Increased intraocular pressure secondary to orbital venous congestion and glaucoma

●Venous stasis retinopathy

●Vitreous hemorrhage

●Proliferative retinopathy

●Ischemic optic neuropathy

●Exudative retinal detachment

●Rare ophthalmologic complications such as choroidal effusions and angle closure glaucoma

DIFFERENTIAL DIAGNOSIS — Other disorders that may be considered in patients with CCF include any process exerting a mass effect on the cavernous sinus (table 1). These include a primary intracranial tumor, lymphoma or other local or distant metastatic tumors, aneurysm, carotid dissection, cavernous sinus thrombosis, infection, Tolosa-Hunt syndrome, orbital pseudotumor, vasculitis, and sarcoidosis. Of these conditions, tumors are the most common.

In addition to these structural compressive lesions, painful ophthalmoplegia can also be caused by ophthalmoplegic migraine, giant cell arteritis, or a diabetic cranial nerve palsy. Patients with pain, proptosis, chemosis, and injection may be suspected of having conjunctivitis and/or orbital cellulitis [13]. When patients present with painful oculomotor (cranial nerve III) palsy, a posterior communicating artery aneurysm will appropriately be considered.

Many of these disorders are discussed in more detail separately. (See "Tolosa-Hunt syndrome" and "Overview of diplopia" and "Septic dural sinus thrombosis" and "Third cranial nerve (oculomotor nerve) palsy in adults" and "Cerebral venous thrombosis: Etiology, clinical features, and diagnosis", section on 'Syndromes associated with isolated sinus or vein thrombosis'.)

Imaging studies will appropriately rule out these conditions as well as reveal and/or suggest the diagnosis of CCF.

DIAGNOSIS AND IMAGING FINDINGS — Conventional digital subtraction angiography is the gold-standard test for diagnosis of CCF. CCFs can be seen on computed tomography (CT), CT angiography (CTA), magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and orbital or transcranial ultrasound. These studies are often ordered as an initial study to exclude other considered diagnoses. (See 'Differential diagnosis' above.)

●CT findings in CCF may include proptosis, expansion of the cavernous sinus and superior ophthalmic vein, enlargement of extraocular muscles, as well as any associated skull fractures. Posterior-draining dural CCFs are less likely to have associated abnormalities on CT or MRI [8]. CTA (using contrast enhancement) appears to be reliable in detecting CCF, and in one study had better sensitivity than MRA at detecting CCFs in the proximal portion of the cavernous sinus [54,55].

●MRI also shows proptosis, expansion of the cavernous sinus and superior ophthalmic vein, and enlargement of extraocular muscles (image 1) [13,56]. MRI may show an abnormal cavernous sinus flow void, a finding specific to CCF [57]. MRI is less sensitive than CT for skull fracture. Use of three-dimensional (3D) time-of-flight MRA can be helpful in the diagnosis of CCF, revealing the shunt with 83 percent sensitivity and 100 percent specificity [58]. MRA using a less common technique, elliptical centric time-resolved imaging of contrast kinetics (EC-TRICKS), has the advantage of providing both spatial and temporal resolution of the arterial and venous circulation [59].

●Transcranial Doppler (TCD) ultrasonography typically reveals increased blood flow velocity and decreased pulsatility index in the carotid siphon in patients with CCF. Abnormalities are observed in both high- and low-flow CCFs, although the findings are less dramatically abnormal in the latter. In general, TCD does not provide details regarding size or venous drainage, although use of color-coding may help distinguish direct from indirect CCF [13,60]. One case series found that TCD was a useful noninvasive means of following patients after treatment [61].

●Conventional digital subtraction angiography is used not only as the gold standard for diagnosis but also to direct treatment.

Angiography should be performed in patients in whom the diagnosis remains uncertain after other radiographic tests, particularly in those patients who are suspected of having a CCF that might be amenable for CCF closure. (See 'Natural history and indications for CCF closure' below.)

A protocol that includes selective injections of both left and right internal and external carotid arteries along with the ipsilateral vertebral artery, ascending pharyngeal artery, middle and accessory meningeal arteries, and proximal and distal internal maxillary arteries is often required to assess size and bilaterality and to identify feeding vessels and drainage pattern [10,62].

Certain angiographic patterns (in particular, cortical venous drainage) are associated with a risk of intracranial hemorrhage [6-8,39,47,63]. Pseudoaneurysm formation, varix of the cavernous sinus, and venous thrombosis remote to the CCF are additional angiographic features that suggest a high risk for intracranial hemorrhage [63,64].

Angiography in this setting often includes a temporary balloon occlusion of the internal carotid artery (ICA) with assessment for clinical symptoms and collateral flow patterns. The patient's ability to tolerate occlusion can be important in assessing the risks of potential therapeutic interventions that may involve sacrifice of the ICA [14].

TREATMENT — The management of patients with CCF includes monitoring of ophthalmologic status, treatment of ophthalmologic complications, and closure of the CCF.

Natural history and indications for CCF closure — Treatment decisions require multiple considerations: the classification of the CCF along with the complexity of the angioarchitecture, the nature of the symptoms, and the risk of future visual and neurologic morbidity.

Because direct high-flow CCFs are unlikely to close spontaneously, and patients are generally very symptomatic and at risk of progression with attendant morbidity, most direct CCFs should be closed [65]. Approximately 20 percent of direct CCFs require emergent treatment secondary to profound decrease in visual acuity, rapid increase in intraocular pressure, elevated intracranial pressure, or bleeding.

By contrast, many (20 to 60 percent) indirect (dural) CCFs will close spontaneously [13,66]. Patients with neurologic symptoms and/or cortical venous drainage on neuroimaging studies are at risk of intracranial hemorrhage and should be considered for closure. Additional indications for treatment include progressive vision loss, as well as proptosis and ophthalmoplegia if severe [36,67]. Patients with milder symptoms can be watched, but close follow-up with serial examinations that include vision tests, measurement of intraocular pressure, and funduscopic examination are advised [11]. The frequency of follow-up as well as the need for additional imaging depends on the severity and evolution of the signs and symptoms as well as the rate of progression. Patients with unclosed dural CCF can experience severe complications if they undergo ocular surgery for other indications (eg, cataract surgery) [68,69].

Techniques for closure — In general, endovascular obliteration is the preferred approach for closure of CCFs. Surgery and other interventions can be considered when endovascular treatment is not possible or is unsuccessful. Some patients with dural CCF are treated with manual vascular compression.

Endovascular approaches — Endovascular treatment of CCFs may use an arterial or venous approach.

For direct CCFs, successful closure rates of 55 to 99 percent have been reported using one or more endovascular techniques [5-7,64,65]. However, this is accompanied by complications (internal carotid artery [ICA] occlusion, cerebral infarction, worsened ocular palsy) in 10 to 40 percent. For indirect (dural) CCFs, the reported cure rate with endovascular treatment is 70 to 90 percent, with a complication rate of 2 to 5 percent [10,12,65,70,71].

●Transarterial embolization – Transarterial embolization is the preferred strategy for most direct CCFs [6,7,72,73]. The goal is to close the fistula while preserving flow within the ICA. Detachable balloons, platinum coils, polyvinyl alcohol particulates, and liquid adhesives have been used to close the fistula using superselective microcatheters placed in the fistula. Treatment may require more than one procedure [7,64]. Stenting, alone or with coil placement, has also been employed successfully in some direct CCFs [7,74-78].

In some patients, a decision may be made to occlude the ICA itself with either balloon or coils. This may be a planned strategy (eg, if there is a large defect) or may follow an attempted fistula occlusion that is complicated by balloon or coil prolapse into the ICA that places the patient at high risk for future thromboembolic stroke [6,14]. Temporary balloon occlusion of the ICA should be performed beforehand to assess the risk of this approach (see 'Diagnosis and imaging findings' above). However, even patients who appear to tolerate temporary balloon occlusion of the ICA have a substantial risk of cerebral infarction when the ICA is occluded.

A transarterial embolization approach is more difficult in indirect CCFs because arterial feeders are small, tortuous, and often multiple [65]. However, it may be used for indirect CCF, sometimes in combination with transvenous embolization in CCFs with external carotid artery supply (Barrow type C or D). polyvinyl alcohol particles or liquid adhesive agents are typically used in this setting.

Complications of transarterial embolization include migration of embolic material into the distal intracranial circulation, causing cerebral ischemia or infarction [5,14,49,79]. The use of anticoagulation during the procedure and antiplatelet therapy afterward may reduce the risk of these events [7]. The arterial wall may also be injured, causing arterial dissection or pseudoaneurysm formation [5,14,64,79]. The latter is relatively common but is of uncertain pathologic significance.

●Transvenous embolization – Transvenous embolization is generally used as a first treatment approach for indirect CCF, particularly those fed via branches of the ICA, and may also be used for direct CCF when the transarterial approach fails or is incompletely successful [10-12,65,71,80]. If necessary, transarterial embolization of accessible feeders may be undertaken before or after venous occlusion. Access for transvenous embolization can be obtained through the transfemoral or transjugular routes [12,70,71,81,82]. Alternative approaches include direct surgical access to the petrosal sinuses [83], superior ophthalmic vein (picture 4) [11,12,70,80,84], inferior ophthalmic vein [85], and pterygoid plexus [86]. Thrombosis is achieved using Guglielmi detachable coils, fibered microcoils, polyvinyl alcohol particulates, cyanoacrylate glue, absorbable gelatin sponge, or detachable balloons.

Transvenous embolization may be complicated by cerebral ischemia or infarction if embolic material migrates across the fistula; subarachnoid or intracerebral hemorrhage, sinus rupture, extradural extravasation of contrast, and cranial nerve palsies may also result [10,11,39,70]. The induction of cavernous sinus thrombosis is associated with transient worsening of symptoms in many patients. As an example, transient worsening of ophthalmoparesis (usually sixth nerve palsy) has been reported in up to 42 percent of patients [82].

Neurosurgery — Surgical treatment of CCFs may be indicated when endovascular treatment is not possible or unsuccessful [5]. Techniques may include placement of packing within the cavernous sinus to occlude the fistula, suturing or clipping the fistula, sealing the fistula with fascia and glue, and/or ligation of the ICA.

Surgical treatment of CCFs is often associated with occlusion of the ICA [14,65,87,88]. A temporary balloon occlusion of the ICA during angiography should be carried out to assess the risk when carotid occlusion is either planned or assessed to be a potential complication. However, cerebral ischemia and infarction may result from this event even when temporary balloon occlusion suggests that collateral flow is adequate. In some cases, surgeons may perform an external to internal carotid artery bypass to ameliorate the risk of cerebral infarction.

In small case series, cure rates of 30 to 100 percent are reported with surgical treatment of CCFs [14,65,87,88].

It is difficult to estimate complication rates of surgical treatment of CCFs from literature reports. Although reviewers suggest that it is high compared with other treatment modalities, patients undergoing surgery may be higher-risk patients than those undergoing other interventions.

Stereotactic radiosurgery — Radiosurgery is indicated when an endovascular approach is not feasible and surgical intervention is difficult or risks significant morbidity [89]. Radiosurgery produces long-term obliteration of dural CCFs in 75 to 100 percent of patients; however, there is a significant latency of several months, even a few years, to the full therapeutic effect [65,90-92]. Radiosurgery should not be considered as a sole modality in those patients requiring immediate treatment, but may follow endovascular or surgical interventions if they are unsuccessful or partially effective [49,91-94]. Radiosurgery can also be considered as a sole treatment modality for older patients with nondisabling symptoms [90].

Stereotactic radiotherapy requires careful consideration of lesion size and complexity. Generally, a dose of 10 to 40 Gy is delivered to the involved area using multiple isocenters [95]. Prior to radiation, the size of the lesion is often minimized using endovascular or neurosurgical treatments to limit the total dose delivered [49].

Stereotactic radiosurgery may result in dose-related neurologic injury, which may be delayed from treatment. The exact frequency of complications is unknown. Complications of stereotactic radiotherapy to the cavernous sinus include delayed carotid stenosis, oculomotor palsies, and facial numbness [96]. Radiation-induced injury to the optic nerve is relatively rare with radiation dose of less than 50 Gy. (See "Delayed complications of cranial irradiation", section on 'Optic neuropathy'.)

Manual vascular compression — While we do not use this technique, some case series in the literature report that some dural CCFs may close with manual vascular compression of the ipsilateral carotid artery. It is believed that reduction of flow produced by this maneuver promotes thrombus formation within the cavernous sinus. One protocol suggests 30 seconds of manual compression of the ipsilateral carotid artery performed several times a day for four to six weeks [97]. The function of the contralateral hand is assessed to help detect ipsilateral cerebral ischemia. In two case series, this treatment approach was associated with CCF closure in 7 of 23 and 8 of 23 patients, respectively; however, there were no control groups for comparison [98,99]. In one of these reports, lower ocular pressure, shorter interval between symptoms onset and initiation of compression treatment, and venous drainage via the superior orbital vein rather than the inferior petrosal sinus appeared to predict successful outcome [99].

Manual compression is contraindicated for cases with severe symptoms including vision loss or any neurologic symptoms, high-risk radiographic features (Barrow type D), ipsilateral carotid disease, cortical venous drainage, or a history of cerebrovascular disease [10]. Complications are rare and include stroke, bradycardia, and hypotension.

Ophthalmologic treatment — Generally, medical management of ocular sequelae is recommended. If medical management fails to control the ocular disease, closure of the CCF is recommended before pursuing ocular surgery.

Patients with proptosis should receive ocular lubrication to treat exposure keratopathy [11].

Elevated intraocular pressure, measured in up to two-thirds of patients, can be treated with a topical agent [53]. Acetazolamide, intravenous corticosteroids, and topical b-blockers may be used as adjuncts to reduce intraocular pressure. However, when vision loss is threatened or intraocular pressure remains elevated, CCF closure is the definitive treatment and should proceed without delay. (See "Open-angle glaucoma: Treatment", section on 'Pharmacologic therapies'.)

Ocular surgery is considered after the primary cause has been addressed.

Uncommonly, high-flow CCF may cause vision-threatening proliferative retinopathy. Primarily treating the CCF as opposed to the retinopathy is recommended when possible [11].

An eye patch, opaque contact lens, or occlusion of an eyeglass lens are simple ways to eliminate diplopia. Prism lenses or strabismus surgery may be indicated in other patients. (See "Overview of diplopia".)

PROGNOSIS — After successful closure of direct and dural CCFs, ocular pressure-related symptoms (increased intraocular pressure, chemosis, proptosis) tend to resolve quickly, within hours to days [10,12]. Cranial nerve deficits resolve somewhat more slowly, over weeks, and are persistent in a minority [7,79]. Recovery of vision deficits depends on their pathogenesis, severity, and duration prior to closure [4,39].

Recanalization of successfully closed CCFs occurs only in a minority of patients. While many large case series report no recurrences after treatment [6,12], reports of recanalization requiring repeat intervention are published [64,100]. In one case series, 9 percent of patients with a dural CCF had a subsequent recurrence [71].

SUMMARY AND RECOMMENDATIONS

●Carotid-cavernous fistulas (CCFs) are classified as direct or high-flow CCFs if they arise from a direct connection between the intracavernous carotid artery and the cavernous sinus, or as indirect, low-flow, or dural CCFs if they result from indirect communication between the cavernous sinus and branches of the internal or external carotid artery within the adjacent dura. (See 'Classification' above.)

●CCFs are acquired vascular lesions that may arise spontaneously or from secondary causes. (See 'Etiology' above.)

Most direct CCFs result from head trauma; they may also occur after rupture of a carotid cavernous aneurysm and can be idiopathic as well.

Dural CCFs arise less commonly in the setting of trauma; preexisting microscopic communications between dural arteries and venous sinuses and venous thrombosis are believed to contribute to their development.

●Direct CCFs present with abrupt onset of bruit, proptosis, diplopia, pain, vision loss, and conjunctival injection. Indirect or dural CCFs typically have a more subacute presentation with a variable combination of these symptoms depending on the pattern of venous drainage. (See 'Clinical presentation' above.)

●Intracranial hemorrhage is an uncommon complication of CCF but can cause substantial morbidity and mortality. This is more common in the setting of cortical venous drainage. (See 'Clinical presentation' above.)

●The differential diagnosis of CCFs includes other conditions affecting the cavernous sinus (table 1). Typically, neuroimaging can exclude these conditions and also suggests the diagnosis of CCF. Cerebral angiography is required in most patients to diagnose, fully characterize the CCF, and direct its treatment. (See 'Differential diagnosis' above and 'Diagnosis and imaging findings' above.)

●We suggest closure of the CCF for patients with direct CCFs and also those with indirect CCFs that either place the patient at risk for intracranial hemorrhage or are associated with progressive vision loss, severe proptosis, or ophthalmoparesis (Grade 2C). Most patients will receive endovascular treatment; however, this is determined based upon the angiographic features of the fistula and its feeding and draining vessels. (See 'Treatment' above.)

●Patients whose CCF is not closed should be followed closely for the development of ophthalmologic complications. The frequency of follow-up, as well as the need for additional imaging, depends on the severity and evolution of the signs and symptoms as well as the rate of progression. (See 'Treatment' above.)

●Elevated intraocular pressure can also be treated medically; however, the definitive treatment of elevated intraocular pressure is CCF closure, which should proceed in all patients with elevated intraocular pressure that cannot be lowered easily and in patients with threatened vision loss. (See 'Ophthalmologic treatment' above.)