Endovascular management of carotid-cavernous fistulas:
When an abnormal connection happens between either of the carotid arteries and the veins just behind the eye, it is called a carotid cavernous fistula.
Because the carotid arteries have a greater pressure of blood flow than do the veins, the rush of blood prevents the veins that serve the eyes from draining properly.
The blood pressure starts to build up in the eye, causing it to bulge. The eye turns red. As the condition gets worse, a person may start losing his or her vision. Without treatment, the sight can be lost in that eye.
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.
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.
Coil Embolization for Carotid Cavernous Fistulas
(pictorial decription of the endovascular management of CCF with coils, balloons, glue and stent). Angiogram
Treating a carotid cavernous fistula with embolization involves placing small platinum coils where the abnormal connection is. This separates the blood flow of the carotid arteries from that of the veins. As a result, the blood can drain properly from the eyes.
Coil embolization is done in an angiography suite. While the patient is given a general anesthetic, the procedure doesn’t require any incision into the head or skull.
During the procedure, a small tube is placed through an artery in the groin. The tube is advanced up to the arteries in the neck. Another smaller tube is threaded through the first one. Small platinum coils are delivered to the abnormal connection through the second tube. The coils separate the blood flowing in the arteries from the blood flowing in the veins.
Coil embolization treatment often completely reverses the disabling symptoms in the eye, if treated early enough.
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.