Third nerve palsy due to a carotid cavernous fistula without external eye signs

An elderly, hypertensive white female presented with acute left-sided facial pain and a left pupil-involved third nerve palsy. She had no history of head trauma. The remainder of the ocular exam was normal, and there was no evidence of proptosis, conjunctival injection or chemosis, or increased intraocular pressure. A computed tomographic scan of the head suggested an enlarged cavernous sinus on the left side. Cerebral angiography revealed a posterior draining carotid-cavernous fistula. A spontaneous carotid-cavernous fistula should be considered in the differential diagnosis of any ocular motor palsy, and may present without external eye signs if the predominant venous drainage is posterior rather than anterior through the superior opthalmic vein.