Dural Carotid-Cavernous Fistulas: Epidemiology, Clinical Presentation, and Management

Dural arteriovenous fistulas of the cavernous sinus are no longer difficult to diagnose or treat. Specific ocular manifestations allow these fistulas to be diagnosed clinically. Noninvasive imaging techniques can be used to confirm the diagnosis. The most common treatment is endovascular occlusion of the lesion via a transarterial or transvenous route. Manual compression of the ipsilateral internal carotid artery in the neck or radiation therapy is appropriate in selected cases. Regardless of the treatment used, the fistula can be closed completely in most cases, resulting in restoration of normal orbital and intracranial blood flow and resolution of visual deficits.

A carotid-cavernous sinus fistula (CCF) is an abnormal communication between the cavernous sinus and the carotid arterial system. CCFs can be classified by cause (traumatic vs spontaneous), velocity of blood flow (high vs low flow), and anatomy (direct vs dural, internal carotid vs external carotid vs both).

Some fistulas are characterized by a direct connection between the cavernous segment of the internal carotid artery and the cavernous sinus. These fistulas are usually of the high-flow type. They are called direct CCFs and are most often caused by a single, traumatic tear in the arterial wall or at times by the rupture of an intracavernous aneurysm. Other CCFs are dural. Many of these lesions are actually congenital arteriovenous fistulas that develop spontaneously, often in the setting of atherosclerosis, systemic hypertension, connective tissue disease, and during or after childbirth. Dural CCFs consist of a communication between the cavernous sinus and 1 or more meningeal branches of the internal carotid artery ( Fig. 1 ), the external carotid artery ( Fig. 2 ), or both ( Fig. 3 ). Of these, fistulas involving branches from both the internal and external carotid arteries are the most common. These fistulas usually have low rates of arterial blood flow. In this article, the author discusses the pathogenesis, causes, clinical manifestations, diagnosis, treatment, and prognosis of dural CCFs.

Pathogenesis

Dural CCFs usually become symptomatic spontaneously. The pathogenesis of these fistulas is somewhat controversial. One hypothesis is that spontaneous dural CCFs form after the rupture of 1 or more of the thin-walled dural arteries that normally traverse the cavernous sinus. According to this hypothesis, after rupture, extensive preformed dural arterial anastomoses not directly involved in the fistula dilate and contribute collateral blood supply, resulting in an angiographic appearance indistinguishable from that of a congenital vascular malformation. Indeed, sequential arteriography demonstrates that the feeder vessels of dural CCFs change with time as the vessels spontaneously open and close. Although this theory is favored by some investigators, it fails to explain why spontaneous dural CCFs are more common in elderly women than in men. A second theory for the origin of dural CCFs is that most develop in response to spontaneous venous thrombosis in the cavernous sinus and represent an attempt to provide a pathway for collateral venous outflow. Most investigators favor this theory because it also explains the pathogenesis of arteriovenous fistulas that develop in the sigmoid and other dural sinuses.

Although many patients who develop a dural CCF are otherwise perfectly healthy, certain factors seem to be predisposed to the development of this lesion. These factors include pregnancy, systemic hypertension, atherosclerotic vascular disease, connective tissue disease (eg, Ehlers-Danlos syndrome type IV), and minor trauma ( Fig. 4 ).

Clinical manifestations

Dural CCFs usually occur in middle-aged or elderly women, but they may produce symptoms in either gender at any age, even in childhood or infancy. The symptoms and signs produced by these lesions are influenced by several factors, including the size of the fistula, the location within the cavernous sinus, the rate of flow, and especially the drainage pattern.

Posteriorly Draining Fistulas

When dural CCFs drain posteriorly into the superior and inferior petrosal sinuses, they are usually asymptomatic. In some cases, however, such fistulas produce a cranial neuropathy, such as a trigeminal neuropathy, facial nerve paresis, or an ocular motor nerve paresis. In most of these cases, there is no evidence of orbital congestion.

In most cases of ocular motor nerve paresis caused by a posteriorly draining dural CCF, the onset of the paresis is sudden, and only one of the ocular motor nerves is affected. The oculomotor nerve is most often affected, and the resulting paresis may be complete with the involvement of the pupil, incomplete with pupil involvement, or incomplete with pupil sparing ( Fig. 5 ). In almost all cases, the paresis is associated with ipsilateral orbital or ocular pain, a presentation that initially suggests an intracranial aneurysm. The correct diagnosis in such cases is not evident until cerebral angiography is performed. In other cases, the posteriorly draining fistula produces an abducens or trochlear nerve paresis, again usually associated with ocular or orbital pain.

The cranial neuropathies that are caused by a posteriorly draining dural CCF usually are the initial sign of the fistula. In many of these cases, failure to diagnose and treat the fistula leads eventually to a change in the direction of the flow of blood in the fistula. The flow becomes anterior, and patients develop evidence of orbital congestion. In other cases, the blood flow in the fistula is initially anterior, producing orbital manifestations. With time, however, the anterior drainage ceases, and posterior flow is associated with the development of the cranial neuropathy.

Dural fistulas that drain posteriorly sometimes cause brainstem congestion that may be associated with neurologic deficits. In addition, such fistulas rarely may produce intracranial hemorrhage.

Anteriorly Draining Fistulas

Dural CCFs that drain anteriorly usually produce visual symptoms and signs. In the mildest cases, there is redness of one or, rarely, both eyes caused by dilation and arterialization of both conjunctival and episcleral veins ( Fig. 6 ). In these cases, the appearance may suggest a primary ocular disorder, such as conjunctivitis, episcleritis, or thyroid eye disease; however, a careful examination of the dilated vessels usually demonstrates a typical tortuous corkscrew appearance that is virtually pathognomonic of a dural CCF ( Fig. 7 ). There also may be minimal eyelid swelling, conjunctival chemosis, proptosis, or a combination of these findings. Diplopia from abducens nerve paresis may be present ( Fig. 8 ). The ocular fundus may seem normal, or there may be mild dilation of retinal veins.

In more advanced dural CCFs, particularly those with a high rate of flow, the symptoms and signs are identical with those in patients with a direct CCF. In these cases, signs of orbital congestion, including proptosis, chemosis, and the dilation of conjunctival vessels, are obvious and severe ( Fig. 9 ). Diplopia may result from ophthalmoparesis caused by ocular motor nerve pareses, orbital congestion, or both mechanisms, and there may be significant periorbital or retro-ocular discomfort or pain, initially suggesting an inflammatory process or even the Tolosa-Hunt syndrome. Some patients develop facial pain, facial weakness, or both. Raised episcleral venous pressure may produce increased intraocular pressure that occasionally is quite high. Angle-closure glaucoma may develop from elevated orbital venous pressure, congestion of the iris and choroid, and forward displacement of the iris-lens diaphragm. In other cases, chronic ischemia produces neovascular glaucoma. Ophthalmoscopic abnormalities include venous stasis retinopathy with retinal hemorrhages, central retinal vein occlusion, proliferative retinopathy, retinal detachment, vitreous hemorrhage, choroidal folds, choroidal effusion, choroidal detachment, or optic disk swelling ( Fig. 10 ).

Visual loss, although less frequent than in patients with direct CCFs, occurs in up to 30% of patients with dural CCFs. It may be caused by ischemic optic neuropathy, chorioretinal dysfunction, or uncontrolled glaucoma.

The ocular manifestations of unilateral dural CCFs are almost always ipsilateral to the fistula, but they may be solely contralateral or bilateral ( Fig. 11 ). When unilateral fistulas cause bilateral manifestations, there is a high probability that the fistula is draining into cortical veins ( Fig. 12 ).

Although most dural fistulas are unilateral, bilateral spontaneous dural fistulas do occur. Patients with bilateral dural CCFs often have severe systemic hypertension, atherosclerosis, or some type of systemic connective tissue disease, such as Ehlers-Danlos syndrome type IV. Most patients with bilateral dural CCFs have bilateral findings; however, some patients with bilateral fistulas have only unilateral signs.

In some instances, dural CCFs drain both anteriorly and posteriorly. In most of these cases, the only manifestations are those related to the anterior drainage; however, some patients develop manifestations from the posterior drainage, such as facial nerve paresis or acute hemiparesis associated with neuroimaging evidence of brainstem congestion.

Clinical manifestations

Posteriorly Draining Fistulas

Dural fistulas that drain posteriorly sometimes cause brainstem congestion that may be associated with neurologic deficits. In addition, such fistulas rarely may produce intracranial hemorrhage.