Indirect Carotid-Cavernous Fistula
- There are 2 types of carotid-cavernous fistulas (CCF): the direct (high-flow) type and the indirect (low-flow) type.
- The direct CCFs can be traumatic or spontaneous (ruptured cavernous carotid aneurysm, less likely congenital connections that can open up in the setting of collagen vascular disease, hypertension or childbirth) in etiology and are associated with the classic clinical triad of chemosis, pulsatile exophthalmos, and ocular bruit.
- Indirect CCFs have a more gradual onset, with generally a milder presentation. They often do not demonstrate the classic triad of symptoms. Instead, patients usually present with chemosis. Bruit and pulsating exophthalmos are absent.
- Key Diagnostic Features: Proptosis, stranding of retrobulbar fat, and extraocular muscle engorgement are typical. Minimal preseptal soft tissue swelling will also be seen. Fullness in the region of the cavernous sinus is often seen in direct CCFs. No such fullness is seen in indirect CCFs. MRA/CTA images will demonstrate flow-related signal/early opacification of the ipsilateral cavernous sinus and superior ophthalmic vein. DSA remains the gold standard to demonstrate the direct/indirect CC fistula. Indirect CC fistulas are typically dural av fistulas (as in our case).
- DDx: Cavernous sinus thrombosis
- Rx: Embolization (transarterial or transvenous), occasionally observation in cases of indirect CCFs.
