Primary oculomotor nerve synkinesis caused by an extracavernous intradural aneurysm.

Primary oculomotor nerve synkinesis is almost always caused by an intracavernous meningioma or aneurysm. We treated a patient who had signs of primary oculomotor nerve synkinesis from an unruptured extracavernous aneurysm located at the junction of the internal carotid artery and the posterior communicating artery. The aneurysm was successfully clipped, resulting in some improvement in ocular motility and alignment. Although most aneurysms affecting the subarachnoid portion of the oculomotor nerve cause an acute, painful oculomotor nerve paresis, such aneurysms may rarely produce painless primary oculomotor synkinesis and therefore should be considered in the differential diagnosis of this phenomenon.