Carotid-Cavernous Fistula

Updated: Jan 22, 2021
Author: Michael G Nosko, MD, PhD; Chief Editor: Brian H Kopell, MD 

Overview

Practice Essentials

The carotid-cavernous fistula (CCF) is a specific type of dural arteriovenous fistula characterized by abnormal arteriovenous shunting within the cavernous sinus. CCFs are classified as either direct or dural(indirect). Direct CCFs are high-flow fistulas with a direct connection between the internal carotid artery (ICA) and the cavernous sinus. Dural CCFs are low-flow fistulas resulting from communications of cavernous arterial branches and the cavernous sinus.[1, 2, 3, 4, 5, 6, 7]

Case reports of dural arteriovenous fistulas were first published in the 1930s. The clinical presentation was recognized, but the pathophysiology was not well understood. During the 1970s and 1980s, the anatomy was further elucidated. Barrow and associates developed the current classification system of caroticocavernous fistulas in 1985.[8, 9]

The cavernous sinus is a network of venous channels traversed by the intracranial portion of the internal carotid artery. The internal carotid artery gives rise to several intracavernous branches. These are the meningohypophyseal and inferolateral trunks. These vessels branch to provide arterial blood to the nerves and dura of the cavernous sinus and the pituitary gland. The external carotid artery provides several branches to the dura of the cavernous sinus and forms anastomoses with the branches of the internal carotid artery.

Classifications

CCFs can be classified based on the hemodynamic properties, etiology, or anatomy of the shunt. Hemodynamically, they are classified as low flow or high flow. They may occur following a trauma or spontaneously. Anatomically, they are classified as type A through type D, as follows:

  • Type A fistulas consist of a direct connection between the intracavernous internal carotid artery and the cavernous sinus. They usually are high-flow and high-pressure fistulas.
  • Type B fistulas consist of a dural shunt between intracavernous branches of the internal carotid artery and the cavernous sinus.
  • Type C fistulas consist of a dural shunt between meningeal branches of the external carotid artery and the cavernous sinus.
  • Type D fistulas are a combination of types B and C, with dural shunts between internal and external carotid artery branches and the cavernous sinus.
  • Types B, C, and D tend to be lower-flow and lower-pressure fistulas with a slower progression of signs and symptoms.

Causes

Direct CCFs result from a traumatic tear in the artery from a skull base fracture, from an acceleration-deceleration force (eg, motor vehicle accident), or from an iatrogenic injury after an endovascular intervention or a trans-sphenoidal procedure. They can also occur spontaneously after rupture of an intracranial aneurysm or weakening of the arteries.[3]  Karaman et al reported on a carotid-cavernous fistula secondary to blunt trauma after functional endoscopic sinus surgery.[10]  

Indirect CCFs result from a dural branch rupture of the carotid artery caused by a genetic condition or a comorbidity such as hypertension.[3]

Blunt head injury can lead to shearing of intracavernous arteries, causing the development of a fistula. Penetrating head injury can lead to fistula formation by direct laceration of intracavernous vessels.

Spontaneous fistula formation has been associated with (1) ruptured intracavernous aneurysm, (2) fibromuscular dysplasia,[11]  (3) Ehlers-Danlos syndrome and other collagen vascular diseases, (4) atherosclerotic vascular disease, (5) pregnancy, and (6) straining.

Signs and symptoms

Onset is usually sudden. Direct carotid-cavernous fistulas are characterized by the triad of pulsatile proptosis, chemosis, and intracranial whistling. There is severe conjunctival congestion, hemorrhagic chemosis, ptosis, and pulsatile proptosis accompanied by a whistling. Painful ophthalmoplegia may be present, with the most common being VI nerve palsy. In cases of indirect carotid-cavernous fistulas, there is moderate ocular congestion, mild proptosis, and ocular pulsation on aplanotonometry.[2, 3, 12]  Arterialization of episcleral veins is shown in the image below. Bruit and headache also may be present upon clinical presentation.

(The image below depicts a type D carotid-cavernous fistula.)

Type-D caroticocavernous fistula: the eye demonstr Type-D caroticocavernous fistula: the eye demonstrates proptosis, chemosis, and scleral edema. The patient is unable to close the eye, exposing the cornea to dehydration and potential trauma.

A carotid-cavernous fistula results in high-pressure arterial blood entering the low-pressure venous cavernous sinus. This interferes with normal venous drainage patterns and compromises blood flow within the cavernous sinus and the orbit, as depicted in the diagram below.

This is a diagrammatic representation of the 4 typ This is a diagrammatic representation of the 4 types of caroticocavernous fistulas. ICA is the internal carotid artery; ECA is the external carotid artery.

A CCF is not a life-threatening disease. The risk of visual loss and the severity of associated symptoms must be evaluated to determine the appropriate degree and timing of intervention. 

Workup

Complete ophthalmologic workup includes visual acuity, pupillary function, intraocular pressure. funduscopy (direct and indirect), and gonioscopy.

Diagnostic tests and imaging for a CCF include the following[3] :

  • Cerebral angiography (see the image below), which is considered the gold standard.
  • Tonometry and pneumotonometry, which may show increased ocular pulse amplitude on the side of the fistula.
  • B-scan or color Doppler ultrasonography, which will identify a dilated superior ophthalmic vein or orbital congestion.
  • CT or MRI, which may reveal a dilated superior ophthalmic vein, orbital congestion, or enlargement of the extraocular muscles.
  • CT angiography or MR angiography, which can detect visual symptoms of CCFs.

Lab studies include routine preangiography workup to evaluate coagulation and renal function prior to delivering contrast dye (CBC count, platelets, prothrombin time [PT], and partial thromboplastin time [PTT]), electrolytes, blood urea nitrogen (BUN), and creatinine.

(An angiogram of a carotid-cavernous fistula is shown below.)

Panel A is an angiogram of caroticocavernous fistu Panel A is an angiogram of caroticocavernous fistula showing filling of the cavernous and circular sinuses. Panel B shows a post-Guglielmi detachable coil, ie, coiling of the fistula. The red arrow points to coils within the cavernous and circular sinuses after obliteration of the fistula.

In a study of time-resolved magnetic resonance angiography (MRA) in 6 patients with CCFs, typical morphologica findings (including enlargement of the superior ophthalmic vein, exophthalmos) were found in all cases.[13]

A study of 98 suspected cases of CCF evaluated with thin-section MR imaging reported overall accuracy, sensitivity, and specificity of 88.8%, 97.4%, and 83.3%, respectively. Abnormal contour of the cavernous sinus, internal signal void of the cavernous sinus, prominent venous drainage flow, and orbital/periorbital soft tissue swelling were proposed as possible predictive findings.[14]

Treatment

Various options are available for the management of CCFs depending on the flow rate. The goal is to achieve complete occlusion of the fistula while preserving normal ICA flow. In cases of indirect, low-flow fistulas, spontaneous closure is possible.

Endovascular intervention is the first-line treatment of CCFs. For direct, high-flow CCFs, the transarterial route is preferred. Surgical options include suturing or clipping the fistula, packing the cavernous sinus, or ligating the ICA. Radiosurgery is not an option for urgent cases, because it can take months to achieve complete obliteration. For low-flow fistulas, compression treatment is the least invasive opton, consisting of compression a number of times a day for 4-6 weeks to achieve fistula thrombosis.[3]

Type A fistulas rarely resolve spontaneously. Treatment is recommended for intolerable bruit, progressive visual loss, and the cosmetic effects of proptosis. Types B, C, and D fistulas have a higher incidence of spontaneous resolution.

Complications of untreated lesions may include visual loss, cranial nerves paralysis, and the cosmetic concerns of proptosis. 

Type A fistulas usually are approached through the internal carotid artery. A detachable balloon or endovascular coil can then be positioned to occlude the fistula while maintaining patency of the internal carotid artery. Venous approaches through the internal jugular vein and the petrosal sinus may allow access to the fistula from the venous side. Guglielmi detachable coils also may be used and are becoming increasingly popular. Types B, C, and D fistulas have smaller fistulous connections and usually are not amenable to the aforementioned treatment approaches. 

Patients with CCFs generally have a good prognosis. Persistent lesions respond well to intervention. The risk of nonophthalmologic neurologic complications is not significant; however, persistent untreated lesions may cause significant visual complications.

Complications of treatment include the standard complications of cerebral angiography. Arterial and venous compromise also may occur, yielding cerebral or retinal ischemia and resultant infarction.

Prognosis

Although direct carotid-cavernous sinus fistulae rarely reopen after closure using a detachable balloon technique, it is not unusual for dural carotid-cavernous sinus fistulae to recanalize or form new abnormal vessels after embolization. The ocular pulse amplitude should be checked postoperatively in all patients, preferably using a pneumotonometer.

Once a fistula is closed, symptoms and signs usually begin to improve within hours to days. The rate and extent of improvement are associated with the severity of the signs and the length of time the fistula was present.

Preexisting ocular bruit, ocular pulsations, and thrill generally disappear immediately after the surgery.

Eyelid engorgement, conjunctival chemosis, dilated conjunctival vessels, stasis retinopathy, disc swelling, and elevated intraocular pressure generally return to normal within weeks to months.

Most patients with dural carotid-cavernous sinus fistulae are healthy within 6 months after treatment, but patients with direct carotid-cavernous sinus fistulae may not experience complete resolution of proptosis, ophthalmoparesis, and visual loss.[15]

 

DDx

Diagnostic Considerations

Conjunctivitis, thyroid eye disease, or other common ocular conditions share clinical features with carotid-cavernous fistulas. Digital subtraction angiography (DSA) is the gold standard for the diagnosis and classification of CCF.[1]  Failure to differentiate CCF from more common diagnoses can result in a worsening prognosis.[16]

Differential Diagnoses

Workup
 

Workup

Imaging Studies

Direct carotid-cavernous sinus fistulae

Computed tomography (CT) scan, magnetic resonance imaging (MRI), and orbital echography often help to confirm the diagnosis, demonstrating extraocular muscle enlargement, dilation of one or both superior ophthalmic veins, and enlargement of the affected cavernous sinus. [2]

Dural carotid-cavernous sinus fistulae

CT scan, MRI, and orbital echography may help to confirm the diagnosis.

All carotid-cavernous sinus fistulae

The definitive diagnostic test is cerebral arteriography with selective catheterization of the internal and external carotid arteries on both sides, so that all arterial contributions to the fistulae can be visualized.

Intra-arterial subtraction angiography is generally the preferred technique.

 

Treatment

Surgical Therapy

Various options are available for the management of CCFs depending on the flow rate. The goal is to achieve complete occlusion of the fistula while preserving normal ICA flow. In cases of indirect, low-flow fistulas, spontaneous closure is possible.

Endovascular intervention is the first-line treatment of CCFs. For direct, high-flow CCFs, the transarterial route is preferred. Surgical options include suturing or clipping the fistula, packing the cavernous sinus, or ligating the ICA. Radiosurgery is not an option for urgent cases, because it can take months to achieve complete obliteration. For low-flow fistulas, compression treatment is the least invasive option, consisting of compression a number of times a day for 4-6 weeks to achieve fistula thrombosis.[3]

In the acute setting of vision loss and/or paralysis of cranial nerves, glucocorticosteroids (eg, dexamethasone) may be used while waiting for definitive diagnostic studies and treatments.[17]

Type A fistulas rarely resolve spontaneously. Treatment is recommended for intolerable bruit, progressive visual loss, and the cosmetic effects of proptosis.[3]

Type A fistulas usually are approached through the internal carotid artery. A detachable balloon can then be positioned to occlude the fistula while maintaining patency of the internal carotid artery. Venous approaches through the internal jugular vein and the petrosal sinus may allow access to the fistula from the venous side. Guglielmi detachable coils also may be used and are becoming increasingly popular.[17]

Types B, C, and D fistulas have a higher incidence of spontaneous resolution.[3]

Type B, C, and D fistulas have smaller fistulous connections and usually are not amenable to the aforementioned treatment approaches. Carotid self-compression for 20-30 seconds 4 times per hour may lead to thrombosis of the fistula. Patients are instructed to compress the carotid artery on the side of the lesion using their contralateral hand. Should the patient develop cerebral ischemia during the compression, the contralateral hand likely will be affected, releasing the compression.

If compression is not effective or if a more rapid intervention is indicated, selective endovascular embolization of the fistula through the external carotid artery usually is effective. Several choices of embolic material are available, although polyvinyl alcohol usually is preferred.

Occasionally a fistula may require an endovascular approach through the superior ophthalmic vein. This requires surgical exposure of the vein to allow placement of the catheter.

Direct surgical exposure and obliteration of the fistula has been described. This rarely is indicated because endovascular approaches have been developed.

Severely refractory fistulas can be treated by surgical or endovascular sacrifice of the internal carotid artery. This, too, is rarely indicated.

In a study of 38 patients with dural carotid-cavernous fistulas, medical treatment was performed in 16% of patients, external ocular compression in 8%, transarterial embolization in 13%, transvenous embolization in 60%, and radiosurgery in 3%. Clinical cure was achieved in 58% of patients and improvement in 24%; anatomic cure was demonstrated in 68%; and transient worsening or new onset of ocular symptoms was observed in 29%.[17]

In a study of clinical and neuroradiologic results in 13 patients with carotid-cavernous fistulas treated by coiling of the cavernous sinus, there was complete occlusion of the fistula in 7 patients (7/13, 54%) and a resolution of symptoms in 8 patients (8/12, 67%). Coiling was performed with a semicompliant nondetachable balloon inflated in the internal carotid artery. The authors noted that balloon-assisted coiling permitted a clear visualization of the fistula, facilitated coil positioning, and protected the patency of the artery.[18]

Patients usually require a follow-up angiogram to ensure that the fistula has not recurred or that alternate fistulous pathways have not developed.

Complications of untreated lesions may include visual loss, cranial nerves paralysis, and the cosmetic concerns of proptosis.[3]

Patients with CCFs generally have a good prognosis. Persistent lesions respond well to intervention. The risk of nonophthalmologic neurologic complications is not significant; however, persistent untreated lesions may cause significant visual complications.

Complications of treatment include the standard complications of cerebral angiography. Arterial and venous compromise also may occur, yielding cerebral or retinal ischemia and resultant infarction.[17]

Medical Care

Exposure keratopathy may be treated with ocular lubricants, and, in severe cases, a tarsorrhaphy may be needed.

Glaucoma may require treatment with aqueous suppressants and hyperosmotic agents.

Laser peripheral iridectomy may be performed to eliminate the contribution of pupillary block, and cycloplegic agents may be used to encourage a posterior shift of the iris-lens diaphragm.

Laser iridoplasty or goniosynechialysis may help further in opening the angle.

Proliferative retinopathy and neovascular glaucoma may require panretinal photocoagulation.

 

Medication

Medication Summary

The goals of pharmacotherapy are to reduce morbidity and to prevent complications. Medications used to decrease aqueous production include beta-blockers, carbonic anhydrase inhibitors (topical or oral), and alpha2-agonists. 

Beta-adrenergic Blockers

Class Summary

Decrease intraocular pressure (IOP) by reducing the aqueous production.

Timolol ophthalmic (Timoptic, Timoptic XE, Betimol, Istalol)

May reduce elevated and normal IOP, with or without glaucoma by reducing production of aqueous humor or by outflow.

Levobunolol (AKBeta, Betagan)

Nonselective beta-adrenergic blocking agent that lowers IOP by reducing aqueous humor production and possibly increases outflow of aqueous humor.

Carteolol ophthalmic

Selectively blocks beta1-adrenergic receptors with little or no effect on beta2-receptors. Reduces IOP by reducing production of aqueous humor.

Betaxolol ophthalmic (Betoptic, Betoptic S)

Selectively blocks beta1-adrenergic receptors with little or no effect on beta2-receptors. Reduces IOP by reducing production of aqueous humor.

Carbonic Anhydrase Inhibitors

Class Summary

By slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport, it may inhibit CA in the ciliary processes of the eye. This effect decreases aqueous humor secretion, reducing IOP.

Dorzolamide (Trusopt)

Used concomitantly with other topical ophthalmic drug products to lower IOP. If more than one ophthalmic drug is being used, administer the drugs at least 10 min apart. Reversibly inhibits carbonic anhydrase, reducing hydrogen ion secretion at renal tubule and increases renal excretion of sodium, potassium bicarbonate, and water to decrease production of aqueous humor.

Brinzolamide (Azopt)

Catalyzes reversible reaction involving hydration of carbon dioxide and dehydration of carbonic acid. May use concomitantly with other topical ophthalmic drug products to lower IOP. If more than one topical ophthalmic drug is being used, administer drugs at least 10 min apart.

Acetazolamide

Inhibits enzyme carbonic anhydrase, reducing rate of aqueous humor formation, which, in turn, reduces IOP. Used for adjunctive treatment of chronic simple (open-angle) glaucoma and secondary glaucoma and preoperatively in acute angle-closure glaucoma when delay of surgery desired to lower IOP.

Methazolamide

Reduces aqueous humor formation by inhibiting enzyme carbonic anhydrase, which results in decreased IOP.

Alpha-agonists

Class Summary

The exact mechanism of ocular antihypertensive action is not established, but appears to be a reduction of aqueous humor production.

Brimonidine (Alphagan P, Qoliana)

Selective alpha2 receptor that reduces aqueous humor formation and increases uveoscleral outflow.

Apraclonidine (Iopidine)

Reduces elevated, as well as normal, IOP whether or not accompanied by glaucoma. A relatively selective alpha-adrenergic agonist that does not have significant local anesthetic activity. Has minimal cardiovascular effects.