Diagnosis: Carotid cavernous fistula
Findings: Two images from an axial contrast enhanced CT scan of the orbits demonstrate mild bulging of the cavernous sinuses bilaterally and a markedly enlarged left superior ophthalmic vein. A lateral view from a right internal carotid angiogram demonstrates lack of filling of the supraclinoid carotid with early opacification of both cavernous sinuses with multiple draining veins, including the left superior ophthalmic vein.
Discussion: Carotid artery cavernous sinus fistulas can be classified as either DIRECT or INDIRECT. Direct carotid cavernous fistulas are posttraumatic and involve a tear in the wall of the carotid artery as it passes through the cavernous sinus. Indirect carotid fistulas are dural arteriovenous malformations involving meningeal branches of the external and occasionally the internal carotid arteries and the cavernous sinus. Indirect cavernous fistulas are usually spontaneous and occurs in older women. Symptoms include pulsatile exopthalmos, chemosis (Chemosis is the swelling (or edema) of the conjunctiva. It is due to exudation from abnormally permeable capillaries. In general, chemosis is a nonspecific sign of eye irritation. The outer surface covering appears to have fluid in it. The conjunctiva becomes swollen and gelatinous in appearance.) , and occasionally blurred vision. Direct type fistulas have similar but often more dramatic symptoms. CT and/or MR findings include proptosis with a bulging cavernous sinus and a dilated superior ophthalmic vein. MRI may demonstrate abnormal flow voids within or between the cavernous sinuses. Cerebral angiography is diagnostic, and treatment is usually transcatheter embolization.
Aunt Minnie’s Pearls
- Abnormal vascular communication between the internal carotid artery and the veins of the cavernous sinus = carotid cavernous fistula
The cavernous sinus (CS) is one of the paired dural venous sinuses
Abducens nerve (CN6) lies within the cavernous sinus