Asymptomatic Penetration of Oculomotor Nerve by Internal Carotid-Posterior Communicating Artery Aneurysm Presenting Pure Acute Subdural Hematoma: A Case Report

To present a unique case of the internal carotid artery-posterior communicating artery (ICA-PcomA) aneurysm penetrating the oculomotor nerve presenting a pure acute subdural hematoma (ASDH) without any oculomotor dysfunction. A 71-year-old woman presented with a sudden headache and drowsiness. She had no history of head trauma and did not manifest any neurological deficits including oculomotor nerve palsy. Computed tomography (CT) of her head revealed left ASDH. Subsequent CT angiography showed an aneurysm originating from the left ICA with an inferior projection having continuity with the hematoma. Intraoperative inspection revealed ASDH observed mainly in middle fossa and no subarachnoid hemorrhage, while the aneurysm was confirmed to split the oculomotor nerve and to be fixed with the middle fossa. The aneurysm was obliterated by direct clip application and the patient’s postoperative course was uneventful. Oculomotor nerve palsy is an important warning sign of imminent rupture of ICA-PcomA aneurysm. However, we should consider that the ICA-PcomA aneurysm could rupture causing ASDH without any oculomotor nerve palsy, even though the aneurysm penetrated the oculomotor nerve.