Carotid-Cavernous Sinus Fistula

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Arterialized episcleral and conjunctival vessels in low-flow dural carotid cavernous sinus fistula.

Signs and Symptoms: Two distinct types of patients develop carotid-cavernous sinus fistula (CCSF). The first is the patient who suffers significant head trauma, often from an traffic accident. This patient bridges age, race and sex profiles. The second is the patient who develops a CCSF spontaneously. This patient is typically a middle-aged female, often with concurrent hypertension.

Patients who develop a CCSF traumatically have pronounced symptoms and signs. There will be marked congestion of the eyelids, conjunctiva and orbit. There is typically proptosis (which is often pulsatile) and limitation of ocular movement. Also, the patient will experience vision loss from a host of possible causes, including secondary glaucoma, exposure keratopathy, and retinal and optic nerve ischemia.

The signs and symptoms of a spontaneous CCSF--also known as a low-flow fistula or dural sinus fistula--are similar to the trauma-induced disorder, albeit much less pronounced. The patient may experience diplopia and ophthalmoplegia (often from CN VI palsy), tinnitus or orbital bruit, and a red, congested eye that is often mistreated as an ocular infection or inflammation. The conjunctival and episcleral vessels are said to be arterialized. That is, the vessels are dilated and tortuous and have a corkscrew-like appearance. This comes from having high-pressure arterial blood coursing through them. Intraocular pressure is often elevated in the involved eye.

Pathophysiology: The cavernous sinus is a trabeculated venous cavern on each side of the sphenoid sinus. It receives blood from the eye and adnexa via the superior and inferior ophthalmic veins, and drains into the jugular vein via the inferior and superior petrosal sinuses. Coursing through the cavernous sinus are the internal carotid artery (and its dural branches --the meningohypophyseal artery, inferior cavernous artery and McConnell's capsular artery), cranial nerves III, IV, V1 and VI,1 and the oculosympathetic plexus.

A CCSF occurs when there is a rupture within the cavernous sinus of either the internal carotid artery (ICA) or one of its smaller dural branches, resulting in the mixing of high-pressure arterial blood into the low-pressure venous system. Rupture of the ICA itself is typically due to trauma, and the signs and symptoms are pronounced. Rupture of one of the smaller dural branches is typically spontaneous, with milder signs and symptoms. Congenital weaknesses and aneurysms of the smaller dural branches most likely account for rupture. This mixing of high-pressure blood in a low-pressure venous system results in the ocular congestion and conjunctival arterialization as blood flows retrograde to the eye and adnexa. While typically unilateral, the presence of an intercavernous sinus allows for possible bilateral involvement.

The mixing of arterial blood in the venous system can allow the patient to hear his or her own heartbeat. You may hear this orbital bruit by placing a stethoscope over the patient's eye. This further manifests as a pulsatile proptosis. Diplopia and ophthalmoplegia occur due to congestion by blood of the muscles within the orbit or compression of the cranial nerves within the cavernous sinus. Multiple cranial neuropathies may coexist.

Secondary glaucoma develops frequently. As high-pressure blood fills the venous system, there is a subsequent rise in episcleral venous pressure. This, in turn, elevates intraocular pressure.

In some cases, anomalous blood flow can reroute retrograde to the cortical venous system. These patients may seem to have undergone clinical resolution, but now have blood flowing retrograde not to the eye but to the brain. They will develop neurologic deficits, such as headache, that are associated with increased intracranial pressure. This imparts a high-risk situation, as the patient can now possibly develop a fatal intradural hemorrhage.

Management: Suspicion of CCSF is crucial for diagnosis. Many patients with low-flow, or dural sinus, CCSF are misdiagnosed and treated erroneously for infections and inflammations, often for months to years.

Diagnosis is accomplished through neuroimaging and arteriography. Contrast-enhanced CT scan and MRI will demonstrate a dilated superior ophthalmic vein and cavernous sinus. Ultrasonography may also demonstrate superior ophthalmic vein engorgement. Magnetic resonance angiography (MRA) is also very useful in identifying fistulas as well as particular vessel involvement. Arteriography is still the gold standard in identifying CCSF with vessel involvement, but due to a small risk of morbidity and mortality associated with this procedure, we reserve this method for potential surgical cases (direct rupture of the ICA in high-flow CCSF or high-risk dural CCSF).

High-flow CCSF resulting from intracavernous rupture of the ICA requires surgical repair. Therapies include endovascular surgery. Current microcatheter techniques permit access to the cavernous sinus via several routes. The most common involves inserting a catheter through the femoral vein and gaining transvenous access via the inferior petrosal sinus. The surgeon repairs the fistula by occluding the rupture with a detachable balloon, liquid adhesive, polyvinyl alcohol particles or endovascular metallic coils. Trans-venous endovascular therapy is a low-risk treatment that is successful in 90% of all CCSF cases.1,2

Low-flow dural sinus CCSF that occurs spontaneously is very likely to resolve spontaneously as well. In these cases, periodic observation is the best therapy because the relatively low risk of morbidity does not merit the risks associated with neurosurgical repair. However, surgical consultation with a neurosurgeon is appropriate. Manage the resultant complications until they resolve. Only consider neurosurgical repair in cases in which there is strong risk of vision loss (from glaucoma, corneal exposure or posterior segment ischemia), intolerable visual symptoms or appearance, or the development of headache indicating high-risk cortical drainage. Be aware of exposure keratopathy and prescribe artificial tears liberally. Manage diplopia with occlusion therapy. Watch for clinical deterioration that indicates that a high-risk cortical venous drainage has developed. Transvenous endovascular therapy is indicated as well for low-flow dural CCSFs that merit repair.

The main ocular concern in CCSF is the development of secondary glaucoma. This may be difficult to treat because most glaucoma medications only reduce the gap between intraocular pressure and episcleral venous pressure. As the episcleral venous pressure elevates in CCSF, it is very difficult to reduce IOP medically. Prostaglandin-like medications can reduce IOP without involving the episcleral venous system, so these are probably most indicated to manage this type of glaucoma.

Clinical Pearls:

  • Practitioners in virtually every medical specialty will misdiagnose the first case of low-flow dural CCSF that they encounter.
  • Look for the characteristic corkscrew episcleral and conjunctival vessels associated with CCSF. Remember, these findings may be subtle.
  • CCSF is typically not a life-threatening condition.
  • Manage low-flow, spontaneously occurring CCSF conservatively.
  • Consider CCSF in patients with "conjunctivitis" and "inflammation" that does not respond to conventional therapy.
  • Consider CCSF in the differential diagnosis of patients with unilateral red eye and elevated IOP.
  • While low-flow CCSF tends to have low risk of morbidity, the drainage can change from the eye to the cortical venous system. This is indicated by headache and other signs associated with increased intracranial pressure. These patients must undergo neurosurgical repair.

1. Meyers PM, Halbach VV, Dowd CF, et al. Dural carotid cavernous fistula: definitive endovascular management and long-term follow-up. Am J Ophthalmol 2002 Jul;134(1):85-92.
2. Mainar Tello E, Vazquez Anon V, Fages Caravaca EM, et al. Direct carotid cavernous fistulas: endovascular treatment using a detachable balloon. Rev Neurol 2001 Sep 16;33(6):533-6.

Other reports in this section

Eyelids & Eyelashes | Conjunctiva & Sclera | Cornea
Uvea | Vitreous & Retina | Optic Nerve & Brain | Oculosystemic Disease

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