Carotid-cavernous sinus fistula is an abnormal communication between the internal or external carotid arteries and the cavernous sinus. These lesions may be classified based on the following: etiology (traumatic vs spontaneous), velocity of blood flow (high vs low), and anatomy (direct vs dural, or internal carotid vs external carotid).
Carotid-cavernous sinus fistulae occur because of traumatic or spontaneous rents in the walls of the intracavernous internal carotid artery or its branches. This results in short-circuiting of the arterial blood into the venous system of the cavernous sinuses.
Direct carotid-cavernous sinus fistulae, which represent 70-90% of all carotid-cavernous sinus fistulae in most series, are characterized by a direct connection between the intracavernous segment of the internal carotid artery and the cavernous sinus. These fistulae usually have high rates of arterial blood flow and most commonly are caused by a single traumatic tear in the arterial wall.
Dural carotid-cavernous sinus fistulae are characterized by a communication between the cavernous sinus and one or more meningeal branches of the internal carotid artery, external carotid artery, or both. These fistulae usually have low rates of arterial blood flow and almost always produce symptoms and signs spontaneously, without any antecedent trauma or manipulation. The lesions may represent congenital arteriovenous malformations, which develop spontaneously or in association with atherosclerosis, systemic hypertension, collagen vascular disease, pregnancy, and during or after childbirth.
Nearly all patients with a direct carotid-cavernous sinus fistula experience progressive ocular complications if the fistula is left untreated. Increasing proptosis, conjunctival chemosis, and visual loss occur over months to years, with central retinal vein occlusion and secondary glaucoma representing the most severe ocular complications.
Several investigators have reported severe epistaxis and intracerebral hemorrhage, potentially fatal, in patients with traumatic carotid-cavernous sinus fistulae. Subarachnoid hemorrhage also may complicate the course of a traumatic carotid-cavernous sinus fistula. A 3% incidence of spontaneous intracerebral hemorrhage caused by carotid-cavernous sinus fistulae has been reported.
Visual loss, although less frequent than in patients with direct carotid-cavernous sinus fistulae, occurs in 20-30% of patients with dural carotid-cavernous sinus fistulae and may be due to secondary ischemic optic neuropathy, chorioretinal dysfunction, including central retinal vein occlusion, or uncontrolled glaucoma.
While direct carotid-cavernous sinus fistulae generally are associated with trauma or surgical manipulation, dural carotid-sinus fistulae occur more commonly in middle-aged to elderly women.
Traumatic carotid-cavernous sinus fistulae occur more commonly in young individuals.
Dural carotid-cavernous sinus fistulae usually occur in middle-aged to elderly women but may produce symptoms at any age, including infancy.
Elicit history of trauma, recent childbirth, or surgical manipulation.
Elicit history of atherosclerosis, systemic hypertension, collagen vascular disease, pseudoxanthoma elasticum, connective tissue diseases (eg, Ehlers-Danlos syndrome), or pregnancy.
Patients may present with the following ocular complaints:
Ophthalmologic examination findings consistent with carotid-cavernous sinus fistula include the following:
Approximately 25% of carotid-cavernous sinus fistulae occur spontaneously, especially in middle-aged to elderly women, and may be associated with atherosclerosis, systemic hypertension, collagen vascular disease, pregnancy, connective tissue disorders (eg, Ehlers-Danlos syndrome), and minor trauma.
Cerebral trauma accounts for approximately 75% of carotid-cavernous sinus fistulae, with motor vehicle accidents, fights, and falls representing the most common settings. The injuries may be penetrating or nonpenetrating and may be associated with basal or facial skull fracture.
Iatrogenic fistulae have been reported following trans-sphenoidal pituitary surgery, endarterectomy, ethmoidal sinus surgery, and percutaneous gasserian and retro-gasserian procedures.
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.
CT scan, MRI, and orbital echography may help to confirm the diagnosis.
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.
Tonometry (preferably with a pneumotonometer) usually demonstrates greater pulse amplitude on the side of the lesion.
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.
The optimal treatment of a direct carotid-cavernous sinus fistula is closure of the abnormal arteriovenous communication with preservation of internal carotid artery patency. Techniques for achieving this result include surgical repair of the damaged portion of the intracavernous internal carotid artery, electrothrombosis, embolization, or balloon occlusion of the fistula.[3, 4, 5, 6]
Dural carotid-cavernous sinus fistulae may close spontaneously, but, for those lesions causing progressive or unacceptable symptoms and signs, standard embolization or endovascular balloon occlusion is generally performed. If these techniques are unsuccessful, direct surgery on the cavernous sinus may be considered. In cases where anatomy makes standard intravascular approach impossible, the superior ophthalmic vein can be cannulated and a balloon or coil threaded into the area of a direct communication.
Neurosurgical consultation for management of the carotid-cavernous fistula
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.
Clinical Context: May reduce elevated and normal IOP, with or without glaucoma by reducing production of aqueous humor or by outflow.
Clinical Context: Nonselective beta-adrenergic blocking agent that lowers IOP by reducing aqueous humor production and possibly increases outflow of aqueous humor.
Clinical Context: Beta-adrenergic blocker that has little or no intrinsic sympathomimetic effects and membrane stabilizing activity. Has little local anesthetic activity. Reduces IOP by reducing production of aqueous humor.
Clinical Context: Blocks beta1- and beta2-receptors and has mild intrinsic sympathomimetic effects.
Clinical Context: Selectively blocks beta1-adrenergic receptors with little or no effect on beta2-receptors. Reduces IOP by reducing production of aqueous humor.
Decrease intraocular pressure (IOP) by reducing the aqueous production.
Clinical Context: 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.
Clinical Context: 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.
Clinical Context: 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.
Clinical Context: Reduces aqueous humor formation by inhibiting enzyme carbonic anhydrase, which results in decreased IOP.
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.
Clinical Context: Selective alpha2 receptor that reduces aqueous humor formation and increases uveoscleral outflow.
Clinical Context: 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.
The exact mechanism of ocular antihypertensive action is not established but appears to be a reduction of aqueous humor production.
Further outpatient care includes periodic monitoring of the condition.
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.