Abstract
Isolated fourth cranial (trochlear) nerve palsy is an uncommon occulomotor nerve palsy typically secondary to ischemia, inflammation/infection, or mass effect. Due to its positioning within the cavernous sinus, pathology of the deep cerebral venous system would theoretically predispose to palsy of this nerve. We present a case of a patient presenting with isolated trochlear nerve palsy in the setting of angiographically-confirmed direct carotid-cavernous fistula.