A carotid cavernous fistula is an abnormal communication between the carotid arterial system and the cavernous sinus. CCFs can be classified by anatomy (direct or dural), etiology (traumatic or spontaneous) or blood flow velocity (high or low). Carotid cavernous fistulas are usually unilateral, although they may occasionally occur bilaterally or produce bilateral signs.
Direct CCFs represent 70 to 90 percent of all cases. They are often caused by a single traumatic rent in the cavernous segment of the internal carotid artery, resulting in a direct communication between the internal carotid artery and the cavernous sinus. These fistulas—usually high-flow—are more common in younger individuals and occur in the setting of cerebral trauma.
Dural CCFs may develop spontaneously in the setting of hypertension, atherosclerosis, collagen-vascular disease or childbirth. Often low-flow in nature, dural fistulas usually arise from a communication between the meningeal arterial branches and the dural veins. They tend to become symptomatic in middle-aged to elderly women.
Signs and Symptoms
Presenting symptoms of CCFs include diplopia, red eye, headache and vision loss. Patients also may describe subjective ocular bruits as a swishing or buzzing sound. Rarely, patients may report pain in the distribution of the first division of the trigeminal nerve.
Reduced arterial blood flow to the orbit and venous engorgement are responsible for most ocular signs of CCFs. Clinical manifestations include proptosis, arterialization of conjunctival vessels (Fig. 1), conjunctival chemosis, eyelid swelling, ophthalmoplegia (especially involving the abducens nerve) and ocular bruits.
The ocular pulse amplitude is usually widened on the side of the CCF. This increased amplitude, while best measured using a continuously recording tonometer (such as a pneumotonometer), can also be recognized by the increased pulsation of the mires on Goldmann applanation tonometery.1
Elevated IOP secondary to elevated episcleral venous pressure is also a common presenting sign in patients with CCFs.1,2 Ophthalmoscopic abnormalities—more prevalent in patients with direct CCFs—include dilation of retinal veins, intraretinal hemorrhages, mild optic disc swelling and even nonrhegmatogenous retinal detachments and choroidal detachments.
Diagnosis of a direct CCF, especially in the context of trauma, is usually straightforward. Dural CCFs, with their often-indolent course, pose a greater challenge. CCFs often are misdiagnosed as thyroid ophthalmopathy, conjunctivitis or even orbital cellulitis. Unilateral disease should raise suspicion, as a large majority of CCFs are unilateral, while thyroid eye disease is often a bilateral condition. A high index of suspicion for patients presenting with signs and symptoms consistent with CCF will prompt the ophthalmologist to check for an ocular bruit, best auscultated over the affected eye with the bell of the stethoscope.
While cerebral arteriography is the gold standard for evaluating patients with CCF, other techniques, including computed tomography, may also be useful.2 Orbital color doppler may show arterialized flow within the superior ophthalmic vein (Fig. 2). Magnetic resonance imaging can demonstrate engorgement of the superior ophthalmic vein, extraocular muscle enlargement, and dilation of the affected cavernous sinus. And while a diagnostic cerebral angiogram may be more invasive than an MRI, it can occasionally become therapeutic, as irritation of the vessels and compression of the carotid artery may result in closure of the CCF.
Direct CCF. In patients with a direct CCF, consultation and expedient closure of the abnormal communication by a neurosurgeon or neurointerventional radiologist usually is indicated. Complications of an untreated direct CCF include glaucomatous damage, venous stasis retinopathy and central retinal vein occlusion. Less frequently, choroidal detachment or exudative retinal detachment may result from a CCF. Anterior ischemic optic neuropathy also may contribute to vision loss.
Improved endovascular techniques have largely replaced surgical treatment approaches for CCF. The goal of endovascular embolization is to cause thrombosis of the fistula while preserving the patency of the internal carotid artery. Percutaneous transarterial embolization using detachable balloons (preferred) or platinum coils is considered the treatment of choice.3
Other techniques to close the fistula include nonballoon embolization and electrothrombosis. As a last resort, craniotomy with direct surgical repair of the internal carotid artery may be performed.
Complications including stroke—and even death—occur most often when the internal carotid artery is unintentionally occluded. But even when internal carotid artery patency is maintained, new neurological deficits and ocular motor nerve paresis may occur.
Dural CCF. These fistulas can initially be watched for signs of spontaneous closure. Spontaneous closure rates of 10 to 60 percent have been cited in low-flow CCFs.2 But with improved neurointerventional techniques and materials, closure of the abnormal vascular communication via transvenous embolization is gaining acceptance as initial therapy. Transvenous access to the cavernous sinus for placement of coils may be obtained via the inferior petrosal sinus or via the superior ophthalmic vein in the orbit. Indications for intervention include deterioration of vision, intolerable bruit, diplopia or proptosis leading to corneal exposure.2
Angiographic characteristics may also guide decision making. CCFs demonstrating cortical venous drainage are considered “high risk” as they may cause elevated intracranial venous pressure and predispose the patient to cerebral infarction or hemorrhage.4 Patients with such fistulas should be referred for neuroradiological intervention.
Studies also have cited self-carotid compression as a relatively noninvasive method to achieve thrombosis of CCFs.5 In this method, patients are instructed to compress their carotid arteries and jugular veins with their contralateral hands for 10 to 30 seconds several times per hour. Initially, this should be done in the presence of a physician who can monitor for adverse signs such as bradycardia or hypotension. Carotid self-compression should not be performed by patients whose angiogram shows cortical venous drainage or who have experienced a recent decline in visual acuity.
Treatment of Elevated IOP
Topical antiglaucoma medications. Episcleral venous pressure is increased in patients with CCFs, and is cited as the main cause of elevated IOP associated with this condition. Even so, IOP elevations usually respond well to topical antiglaucoma medications. IOP elevation refractory to topical medications may be considered an indication for closure of the CCF, as normalization of IOP usually occurs upon closure of the abnormal communication.
Peripheral iridotomy. Angle-closure glaucoma may occur infrequently in patients with CCF secondary to uveal congestion and forward rotation of the ciliary body. In these patients, a peripheral iridotomy should be considered.
Filtering surgery. Filtering surgery carries risk of complications—including choroidal effusion and hemorrhage—but may be necessary for IOP control in some patients.
Panretinal photocoagulation. Chronic retinal hypoxia infrequently can cause neovascular glaucoma in patients with CCF. Panretinal photocoagulation may be needed in such cases.
With all CCFs, ocular signs and symptoms usually resolve once the fistula is closed. Ocular bruits and ocular pulsations usually resolve immediately. Conjunctival chemosis, conjunctival arterialization, eyelid edema, venous stasis retinopathy, and disc swelling may take weeks or months to normalize. Elevated IOP may normalize immediately following embolization or may take weeks or months to resolve.
A direct CCF usually does not reopen after successful embolization using a detachable balloon, especially when the internal carotid artery remains patent. In contrast, it is not unusual for recanalization to occur after embolization of dural CCFs.
While most patients with dural CCFs are normal within six months after treatment, proptosis and visual loss may never completely resolve in patients with direct CCFs.1
Dr. Khator is a resident at the Friedenwald Eye Institute and Dr. Rismondo is an associate professor at Johns Hopkins University.
1 Miller, N. R. “Carotid-Cavernous Sinus Fistulas,” Walsh and Hoyt’s Clinical Neuro-Ophthalmology, 6th ed. (Baltimore: Lippincott, Williams & Wilkins, 2005) pp. 2263-2296.
2 Keltner, J. L. et al. Ophthalmology 1987; 94(12):1585–1600.
3 Luo, C. B. et al. J Trauma 2004;56(6): 1214–1220.
4 Meyers, P. M. Am J Ophthalmol 2002;134:85–92.
5 Halbach, V. V. et al. Radiology 1987; 163:437–442.