Ann P. Murchison
Jurij R. Bilyk
BASICS
DESCRIPTION
A carotid/cavernous sinus fistula (CCF) is an abnormal communication between an artery and the venous plexus within the cavernous sinus (CS). This can occur spontaneously or secondary to trauma. Fistulas are broadly categorized based on the flow rate (high or low) and more specifically by the feeder vessel(s) (Tables 1 and 2).
Table 1 A simplified schema of CCF, based on clinical findings (1)[C]
| Type | Characteristics | Clinical features |
| High flow | • Usually direct fistulas (Barrow type A) • 70–80% are due to trauma resulting in basilar skull fracture, with a resultant tear in the internal carotid artery • Spontaneous lesions are secondary to aneurysm or atherosclerotic damage • Iatrogenic: Endovascular procedures (including carotid endarterectomy), skull base surgery | • Usually dramatic external signs • Most common in young males • May result in permanent visual loss and neurologic injury • Requires closure |
| Low flow | • Usually indirect fistulas (Barrow type B, C, or D) • Also called “dural-sinus fistula” • Typically fed by a smaller caliber branch of the internal or external carotid artery, or both (e.g., meningeal arteries, ascending pharyngeal artery, etc.) | • Typically subtle, more chronic signs • More common in females >50 years of age • Associated with hypertension, atherosclerosis, and connective tissue diseases • May close spontaneously |
Table 2 The Barrow classification of CCF
| Type | Arterial feeder |
| A | ICA |
| B | Branches of the ICA |
| C | Branches of the ECA |
| D | Branches of both ICA and ECA |
| ICA = internal carotid artery; ECA = external carotid artery. | |
EPIDEMIOLOGY
Incidence
Specific numbers are not known but overall it is a rare entity.
Prevalence
Not known
RISK FACTORS
• Hypertension
• Atherosclerosis
• Collagen vascular disease
• Connective tissue disease (Ehlers–Danlos)
• Pregnancy
• History of carotid artery aneurysm
• History of trauma
Genetics
The genetics associated with collagen vascular diseases, pseudoxanthoma elasticum, and connective tissue diseases would apply in appropriate cases. However, the majority of cases are secondary to hypertension and trauma.
GENERAL PREVENTION
Minimizing risk factors associated with hypertension and atherosclerosis would presumably be beneficial in decreasing the risk of some forms of CCF.
PATHOPHYSIOLOGY
CCF alters the flow dynamics of the skull base. The superior ophthalmic vein (SOV) provides almost exclusive venous drainage of the orbit into the CS. In addition, the venous plexus of the CS communicates with the contralateral CS and the deep cortical veins within the brain. An abnormal communication between an intracranial artery and the venous plexus of the CS creates flow problems in the surrounding anatomy, potentially causing damage intraorbitally and intracranially.
ETIOLOGY
See above
COMMONLY ASSOCIATED CONDITIONS
See the Risk Factors section
DIAGNOSIS
HISTORY
• Presenting symptoms vary widely and depend of the amount of blood flow through the fistula. High-flow fistulas can present with marked proptosis, diplopia, and decreased vision. Low-flow fistulas may only have mild conjunctival injection.
• The patient may have a recent or distant history of trauma, which may or may not have affected the head.
• Complaints of a dull retrobulbar ache or “whooshing” sound in the head may be present.
• In lower flow lesions, the patient’s only complaint may be of a unilateral or, less frequently, bilateral red eye of varying duration, from days to months. Patients may have seen multiple physicians and carry a variety of misdiagnoses, including conjunctivitis, allergic reaction, dry eye, etc. (1)[C].
• Some patients may elicit a history of unilateral glaucoma, often diagnosed at the time of the red eye.
• Double vision. Since the abducens nerve is the most vulnerable cranial nerve within the CS, patients may complain of horizontal, binocular diplopia that is gaze dependent. Vertical diplopia is less common.
• The patient may complain of a bulging eye if proptosis is present.
• Neurologic symptoms (weakness, slurred speech, sensory deficits) are ominous signs of possible posterior cortical venous drainage.
PHYSICAL EXAM
• Decreased vision, dyschromatopsia, and afferent pupillary defect: Usually secondary to vascular compromise of the optic nerve or retina
• Asymmetrically elevated intraocular pressure: Secondary to decreased episcleral venous outflow into a congested orbit
• Conjunctival injection: As the CS becomes arterialized with blood from the feeding vessel(s), the venous outflow of the orbit becomes congested, causing the conjunctival vessels to become dilated and tortuous. At the slit lamp, “corkscrewing” of the conjunctival vessels extending to the limbus may be present.
• Proptosis: As orbital venous congestion develops, the globe becomes anteriorly displaced
• Diplopia: See the History section
• Bruit: A supraorbital bruit may be auscultated in higher flow lesions
• Optic nerve edema
• Central or branch retinal vein occlusion, secondary to venous stasis. Arterial occlusion is less common
• Angle-closure glaucoma from forward rotation of the iris-lens diaphragm (2)[C]
DIAGNOSTIC TESTS & INTERPRETATION
Lab
Initial lab tests
There are no diagnostic lab tests.
Imaging
Initial approach
• Orbital color Doppler ultrasonography: A noninvasive method to detect an enlarged SOV with reversal of flow and an arteriolized wave form. The sensitivity and specificity of this test is unknown, but is probably more reliable in higher flow states.
• CT/CTA: In cases where trauma is involved, this is usually the first imaging study done. Typical findings include an enlarged superior ophthalmic vein (SOV), thickened extraocular muscles and an enlarged CS. The sensitivity of CTA is dependent on the caliber of the fistula.
• MRI/MRA: Similar findings as in CT. MRI may also show slow flow or thrombus formation within the SOV.
• Angiography: This is the gold standard, can diagnose small arterial feeders, and allows simultaneous management by embolization. It is important to perform angiography of the entire cranial arterial system (“six vessel” angiography: Bilateral internal and external carotid arteries as well as vertebral arteries). This modality will also assess any posterior cortical venous outflow. Arteriography alone can be therapeutic for indirect dural fistulas in 20–50% of cases (2)[C].
Follow-up & special considerations
If no posterior cortical venous outflow is present and visual function is not at risk, many patients with low-flow fistulas may be managed conservatively.
DIFFERENTIAL DIAGNOSIS
• Thyroid eye disease
• Idiopathic orbital inflammatory syndrome
• Spheno-orbital mass
• Conjunctivitis
• Episcleritis
• Tolosa-Hunt syndrome (2)[C]
TREATMENT
MEDICATION
First Line
Glaucoma: Treated with topical medications including beta-blocker, alpha agonist, carbonic anhydrase inhibitor, or prostaglandin. An oral carbonic anhydrase inhibitor may also be utilized.
Second Line
• Systemic management of hypertension and hypercholesterolemia
• Exposure keratopathy: Treated with aggressive lubrication or tarsorrhaphy
ADDITIONAL TREATMENT
General Measures
Low-flow fistulas with few clinical manifestations can be observed and may close spontaneously. Carotid massage is an effective measure for the closure of low-flow lesions. The patient is instructed to always use the contralateral hand to perform the massage to minimize the risk of permanent ischemic injury to the brain.
Issues for Referral
• Because of the ocular manifestations, it is common for an ophthalmologist to make the initial diagnosis. All CCFs should be referred to a neurosurgeon or interventional neuroradiologist for angiography and treatment. In appropriate cases where the SOV can be used to approach the CS, an orbital specialist may also be involved.
• Timing of referral is important. Chronic symptomatology is less urgent than more acute manifestations. In acute lesions, the possibility of posterior cortical venous outflow with the attendant risk of hemorrhagic stroke must be considered.
SURGERY/OTHER PROCEDURES
• An endovascular approach using either the arterial or venous system, with embolization of the fistula using a number of materials. These procedures are technically difficult and often require a multidisciplinary approach (3)[C]. An SOV approach through a lid crease incision often requires an orbital surgeon experienced in this procedure.
• Other treatments for CCFs include craniotomy, conventional radiation therapy, stereotactic radiosurgery (3)[C].
IN-PATIENT CONSIDERATIONS
Initial Stabilization
• For trauma patients follow standard protocols.
• Following embolization, the patient should be monitored for an acute exacerbation of orbital signs, which may occur after acute closure of the SOV.
Admission Criteria
Most patients who undergo angiography or endovascular treatment are admitted for 24 h of observation.
IV Fluids
Hydration is necessary to clear the intravenous dye load of angiography.
Nursing
• Management of the angiography cut-down site
• Frequent neurologic checks to rule out cerebral vasospasm
• Observation for any worsening of orbital signs
Discharge Criteria
• Visual function is stable and intraocular pressure is normalizing
• Cut-down site is stable
• No new neurologic signs occur
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patients with CCFs should be seen regularly by their ophthalmologist to have a complete eye exam with monitoring of intraocular pressure, since CCFs can reopen or develop new feeder vessels.
DIET
No specific dietary recommendations
PATIENT EDUCATION
Return with any new recurrent ocular or neurologic symptoms
PROGNOSIS
• Initially, the prognosis for visual function is guarded and dependent on the dynamics of the CCF.
• With successful closure of the CCF, long-term prognosis is good.
COMPLICATIONS
• Loss of vision
• Ocular ischemia, including neovascular glaucoma
• Permanent neurologic sequelae, including stroke
• Death is more often associated with high-flow, direct fistulas.
REFERENCES
1. Chaudhry IA, Elkhamry SM, Al-Rashed W, et al. Carotid cavernous fistula: Ophthalmological implications. Middle East Afr J Ophthalmol 2009;16(2):57–63.
2. Miller NR. Diagnosis and management of dural carotid-cavernous sinus fistulas. Neurosurg Focus 2007;E 23(5):13.
3. Gemmete JJ, Ansari SA, Gandhi DM. Endovascular techniques for treatment of carotid-cavernous fistula. J Neuro-Ophthalmol 2009;29:62–71.
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