Cerebral Aneurysm Arising from Variant Posterior Communicating Artery Lying Lateral to Oculomotor Nerve

In most cases, the posterior communicating artery (PCoA) lies medial to the oculomotor nerve. In this report, a rare case of a ruptured cerebral aneurysm arising from a variant PCoA lying lateral to the oculomotor nerve is described. A 41-year-old woman who had a history of surgical clipping of a right PCoA aneurysm 13 years earlier developed a subarachnoid hemorrhage due to a ruptured left true PCoA aneurysm. Three-dimensional computed tomography angiography showed a small saccular aneurysm arising from the PCoA itself. She underwent surgical clipping via a left frontotemporal craniotomy. Interestingly, the PCoA lay lateral to the oculomotor nerve, and the aneurysm dome projected medially and compressed the oculomotor nerve medially. A slightly angled fenestrated miniclip was applied across the PCoA, followed by reconstruction of the PCoA medial wall and simultaneous obliteration of the aneurysm. Complete aneurysm obliteration and good patency of both the PCoA and perforating arteries were confirmed intraoperatively by indocyanine green videoangiography. The patient's postoperative course was uneventful, and the patient was discharged with no neurologic deficits. Recognizing this anatomic variant is helpful in minimizing the potential complications in microsurgical management around the PCoA and oculomotor nerve. Lateral localization of the P1-2 junction might affect this rare anatomic variant.