Dural carotid-cavernous fistulas arise spontaneously and primarily in elderly women. Dural branches of the internal or external carotid are equally involved, and fistulas often arise spontaneously from both sources. The resulting venous congestion causes an ectasia of the orbital and conjunctival veins that are clearly differentiable from inflammatory hyperemia (large, rope-like conjunctival vessels that contrast with white scleral tissue), as well as chemosis with lid swelling, exophthalmos, retinal vascular dilatation with intraretinal hemorrhages, and elevated intraocular pressure. The latter feature is caused by the marked elevation in episcleral venous pressure that is transmitted directly to the anterior chamber. The elevated pressure in the cavernous sinus causes damage to the third, fourth, and sixth cranial nerves, resulting in diplopia. Frequently, patients hear a pulse-synchronous bruit when background noise is diminished, usually when retiring for the evening, and often apparent with particular head positions, such as sleeping on one side. The elevated venous pressure raises a hurdle for the drainage of aqueous humor, which must pass through the trabecular meshwork and into the episcleral veins. This causes a severe form of secondary glaucoma that is very difficult to manage. During applanation tono-metric measures of the intraocular pressure, the examiner can easily appreciate the strong, pulsating variation in the size of the circle flattened on the corneal surface. In some cases, both eyes are affected by the fistula. CT or MRI scanning will show expansion in the size of the cavernous sinus, the ophthalmic veins, and the extraocular muscles. The exact diagnosis requires cerebral angiography to show the location of the communication. When loss of vision is threatened, a surgical closure of the fistula can be accomplished by transluminal, selective catheterization and embolization of the fistula. This procedure requires the services of an interventional neuroradiologist.
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