||Summary: Carotid Cavernous fistula • Abnormal connection between the internal or external carotid artery and the cavernous sinus, skipping a capillary bed • Arteriovenous fistula: Carotid is the artery and cavernous sinus is the vein • Cranial nerve V1 is often involved, it is free floating in the substance outside of the cavernous sinus Differentiating features: • Can present as red eyed shunt or white eyed shunt • Multiple cranial neuropathies • Horner syndrome could be present • Could be a lesion in internal or external carotid or both leading to dilation of superior ophthalmic vein • Enlarged superior ophthalmic vein represents retrograde flow of arterialized blood into orbit • Episcleral blood vessels dilated and tortuous, called arterialization • Arterialization of the conjunctiva • Episcleral pressure could increase and lead to glaucoma • Elevation of intraocular pressure may occur, there may be retinal venous dilation, a macular edema and retinal hemorrhages, might even be a central retinal vein occlusion. • Afferent and efferent problems • Radiographically: proptotic, ophthalmoplegic, complaining of diplopia Types of carotid cavernous fistulas: • Direct fistula (type A): Direct tear in the internal carotid artery, usually from trauma • Indirect fistula (low-flow fistula, type B, C, or D): non-traumatic, spontaneous in older middle-aged adults and from internal, external or both carotid arteries • Angiogram will determine which type of fistula by visualizing which arteries are involved Diagnosis and treatment: • Patients presenting with these symptoms should be observed for dilation of superior ophthalmic vein • If visible, then angiogram to confirm • Treatment is usually endovascular embolization with coil or onyx • Treatment more imperative when patient is losing vision or in pain
||So today we're going to be talking about the carotid cavernous fistula, CC fistula. A fistula is an abnormal connection between two unlike things, and in this case it's between the carotid artery either the internal or external carotid artery and the cavernous sinus. So, it is a form of an arteriovenous fistula, the artery is the carotid, the vein is the sinus called the cavernous sinus and the fistula means arterialized blood is going to be travelling into the slow flow venous side without a major draining capillary bed. So, as you remember from anatomy, the anatomy of the cavernous sinus here in coronal section, in the wall of the dura of the cavernous sinus, relatively protected, are cranial nerves III, IV, and V, subdivision one (V1). In the posterior cavernous sinus, we have V2, but V3 has already left, it doesn't go into the cavernous sinus and goes out of the foramen ovale. This is the internal carotid artery and VI lives free-floating in the substance of the cavernous sinus so cranial nerve VI is often involved in patients who have carotid cavernous fistulas. Surrounding the internal carotid artery and jumping for a short course on sixth is the ocular sympathetic pathway so we may or may not have pupil involvement from the Horner syndrome and anisocoria that's greater in the dark. So when we have a carotid cavernous fistula the key in differentiating features are the presence of multiple cranial neuropathies, plus or minus the Horner syndrome from the cavernous sinus involvement and because it's a vascular lesion from the carotid, either the internal carotid artery or the external carotid artery or both, the flow will be directed retrograde and anteriorly into the orbit, and that means that the superior ophthalmic vein might be dilated. So if we have a carotid cavernous fistula, the blood, instead of going from the orbit, through the cavernous sinus and back down the petrosal to the jugular, is going anteriorly and that's going to produce an enlarged superior ophthalmic vein and the enlargement of the superior ophthalmic vein represents the retrograde flow of the arterialized blood into the orbit. What that's going to produce is the key and differentiating feature of carotid cavernous fistula if the blood is draining anteriorly. So, on the cornea here, the blood vessels might be dilated. The episcleral blood vessels will be dilated and tortuous to the limbus and they might loop back. The intervening conjunctiva is often clear, and it forms these alternating omega loops (like the Greek letter omega) because the dilation and the tortuosity might make the vessel dilated and tortuous and that, we call arterialization. This arterialization flow is the distinctive finding. In addition, it might cause an increase in episcleral pressure, which would cause glaucoma. So, the elevation of intraocular pressure may occur, there may be retinal venous dilation, a macular edema and retinal hemorrhages, might even be a central retinal vein occlusion. Or, they might have ischemia to the optic nerve. So we can have problems both on the afferent side, loss of vision, ischemic optic neuropathy, macular edema, central retinal vein occlusion, and on the efferent side, cranial verves 3,4, 6 and pupil problems (big pupil from the third nerve palsy, small nerve from the Horner's syndrome) and a dilated superior ophthalmic vein. Radiographically, the patient will be proptotic, ophthalmoplegic, complaining of diplopia So, when we have a carotid cavernous fistula, you can either have a direct fistula, a direct tear in the internal carotid artery (that's normally from trauma); that is a type A fistula. Or, it can be a low-flow fistula. A low-flow fistula is an indirect fistula, it's non traumatic, often spontaneous in older middle-aged people and the low-flow fistulas are either from the internal, external carotid or both, which are the classifications B, C, and D. So, the B, C, and D fistulas are the low-flow, non-traumatic fistulas from either branches of the internal external carotid arteries and the only way to know that is to do an angiogram. So, with any patient who presents with orbital signs, proptosis, arterialization of the conjunctiva, diplopia, afferent and efferent problems or evidence of cavernous sinus involvement, we're going to do an imaging study looking for dilation of the superior ophthalmic vein. If we see that, we're going to perform a catheter angiogram and there's some features on the catheter angiogram that are going to make it absolutely imperative that we discuss treatment which is usually endovascular embolization with coil or onyx or other material and those things are corticovenous drainage, pseudoaneurysm. Those are the things that are going to push us to treatment, if they're losing their vision or have severe pain, those are also indications for doing the treatment. And so, you should know that the carotid cavernous fistula is an arteriovenous fistula, it can present to us in ophthalmology as red eye, it can also drain posteriorly in the petrosal sinus without draining in the superior ophthalmic vein and that's going to produce a white-eyed shunt, a painful progressive sixth is how that normally presents. So, it can be a red-eyed shunt, a white eyed shunt, and all of these need imaging studies, and preferably the gold standard, a catheter angiogram.