Horner syndrome and VI nerve paresis as a diagnostic clue to a hidden lesion.

A 33-year-old man treated elsewhere for an isolated VI cranial nerve paresis underwent an attempted transnasal biopsy of a large space-occupying lesion in the cavernous sinus and petrous apex seen on a CT scan. During the procedure, he developed severe bleeding and hypovolaemic shock. When he came to us 2 years later, he had Homer syndrome along with a mild VI nerve paresis that aided in localizing the lesion to the carotid canal and the posterior cavernous sinus. Digital subtraction angiography revealed a large internal carotid artery aneurysm of the laceral and petrous segments within the carotid canal, mushrooming into the posterior cavernous sinus.