Third nerve paresis caused by vascular compression by the posterior communicating artery.

Objective And Importance: Third nerve paresis frequently occurs because of external compression by an internal carotid-posterior communicating artery aneurysm. We report 1 case of third nerve palsy because of direct vascular compression by the posterior communicating artery.

Clinical Presentation: A 69-year-old man presented to the hospital with the sudden onset of left third nerve palsy and a history of chronic headaches. A cerebral angiogram showed a cavernous aneurysm of the left internal carotid artery as well as a large dilatation of the left posterior communicating artery.

Intervention: A left transylvian approach exposed an infundibulum of the left posterior communicating artery in contact with and creating an indentation on the third cranial nerve. The artery was dissected free of the nerve, and vascular decompression was achieved with complete resolution of the oculomotor nerve paresis.

Conclusion: Third nerve palsy may in some cases result from direct vascular compression by the posterior communicating artery, particularly if associated with a broad infundibulum.