The above axial maximum-intensity projection slab from a CT cerebral angiogram shows dilatation of both superior ophthalmic veins and engorgement of the cavernous sinuses. The appearance is consistent with caroticocavernous fistula. Digital subtraction angiography showed the fistula to be of the indirect (low-flow) type.

Caroticocavernous fistula can be classified as direct (high-flow) or indirect (low-flow). High flow fistulas are due to a direct communication and are usually due to trauma or rupture of cavernous ICA aneurysm. Indirect fistulas are due to communication by multiple dural branches of ECA +/- ICA, and are postulated to occur secondary to cavernous sinus thrombosis with revascularisation.

Endovascular treatment of direct fistulas may be by transarterial (via ICA rent into cavernous sinus) or transvenous (inferior petrosal sinus or superior ophthalmic vein) routes. Indirect fistulas typically require a combined transarterial (closure of feeders) and transvenous (closure of cavernous sinus) approach.

Castillo M. Neuroradiology Companion 3rd edition. Lippincott, Williams & Wilkins 2006
Credit: Dr Laughlin Dawes, Dr Constantine Phatouros