Third cranial nerve palsies

Third nerve palsies can represent a wide variety of pathologic processes, ranging from benign to life threatening. Localization of the causative lesion directs subsequent laboratory testing and imaging studies. The lesion can often be localized based on associated signs and symptoms. The differential diagnosis for an isolated third nerve lesion varies based upon the patient’s age and the relative deficits of extraocular movements and pupillary function. It is imperative that at-risk patients be adequately evaluated for cerebral arterial aneurysm using CTA, MRA, or CCA.