Digital subtraction angiography (not shown) demonstrated 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 revascularization.

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. 

Credit: Dr Laughlin Dawes and Dr Constantine Phatouros.