Failure to demonstrate a direct caroticocavernous fistula due to arterialisation of the ipsilateral cavernous sinus.

We report a woman in whom a small direct caroticocavernous fistula (DCCF) was revealed after successful transarterial occlusion of a contralateral fistula which drained into both cavernous sinuses. We underline that a second smaller fistula can be masked by a contralateral larger one due to the lack of pressure gradient between the internal carotid artery (ICA) and arterialised blood in the ipsilateral cavernous sinus. We suggest that bilateral ICA angiograms should be performed before and after occlusion of all DCCF.