Fig. 17. Left internal carotid angiogram. The internal carotid artery within the cavernous sinus is seen in anteroposterior projection as a dark circle (A) and in lateral projection as an S-shaped structure (B). The fistula (black arrow) in this patient drained anteriorly into the superior ophthalmic vein (double arrow) and inferior ophthalmic vein (white arrow). In the absence of a history of trauma, the presumed etiology of the fistula in this patient was rupture of a preexisting intracavernous aneurysm.