Oculomotor Nerve Palsy caused by the Posterior Communicating Artery with Impending Ruptured Internal Carotid-Posterior Communicating Aneurysm : A Case Report

The sudden onset of oculomotor nerve(OCN)paralysis is a symptom that suggests the impending rupture of a cerebral aneurysm. The mechanism of such OCN paralysis has been proposed as direct compression by an enlarged aneurysm and/or blood leakage from an aneurysm. In this article, we report a rare case of aneurysm enlargement in the posterior communicating(Pcom)artery direction to compress the OCN. A 60‒year‒old woman presented with left OCN paralysis with both ptosis and mydriasis. Although CT did not show any intracranial hemorrhage, CT angiography revealed a left internal carotid‒ Pcom(IC‒PC)aneurysm. We diagnosed it as an impending rupture of the aneurysm that required emergency surgery. Intraoperative findings revealed that the fetal Pcom artery, but not the aneurysm, compressed the OCN. We performed neck clipping and partial wrapping of the aneurysm to change the Pcom artery direction to decompress the OCN. Her symptoms improved after surgery. There was a case report in which the Pcom artery compressed the OCN directly instead of the aneurysm, suggesting that it was caused by an abnormal running of the fetal Pcom artery. In this case, aneurysm clipping reduces the volume of the aneurysm to normalize the Pcom artery direction, resulting in neurovascular decompression of the oculomotor nerve. (Received March 5, 2020;accepted June 24, 2020)