Microvascular decompression for long-standing oculomotor nerve palsy due to compression by fetal-type posterior communicating artery.

Acquired oculomotor nerve palsy is most commonly due to microvascular ischaemia, while symptomatic non-aneurysmal neurovascular compression remains exceedingly rare and often underdiagnosed. We report the case of a woman with a 2-year history of left-sided ptosis and binocular horizontal diplopia. Imaging revealed a neurovascular conflict secondary to a fetal-type posterior communicating artery. Conservative treatments failed, and the patient underwent microvascular decompression (MVD) via a left pterional approach. Decompression was achieved using a dural sling affixed to the internal carotid artery with an aneurysm clip. Postoperative recovery was rapid, with resolution of symptoms by the third week. This case highlights the need to consider neurovascular compression in unexplained or apparent idiopathic third nerve palsy, even years after symptom onset. It also demonstrates that MVD can be effective even in long-standing cases.