Microvascular Decompression for Oculomotor Nerve Palsy Due to Compression by Infundibular Dilatation of Posterior Communicating Artery

BACKGROUND: Oculomotor nerve palsy is occasionally a key indicator of an internal carotid posterior communicating (ICPC) artery bifurcation aneurysm. The interval between the onset of palsy and the time of surgery is considered to be the most important factor affecting recovery from oculomotor nerve palsy. We encountered a rare case of oculomotor nerve palsy due to compression by the infundibular dilatation of the posterior communicating artery (PcomA) rather than by an ICPC aneurysm. CASE DESCRIPTION: We report the case of a 70-year-old woman who presented with pain in the left forehead and left oculomotor nerve palsy with a prominence at the bifurcation of the left internal carotid artery and PcomA on neuroradiologic imaging, indicating a small aneurysm. However, the positional relationship between the bulging lesion and PcomA was not apparent. The intraoperative microscopic view showed that the lesion was an infundibular dilatation of the PcomA rather than an aneurysm, compressing the oculomotor nerve. Microvascular decompression of the lesion resulted in the disappearance of her symptoms after 3 months. CONCLUSIONS: For the treatment of a symptomatic ICPC unruptured aneurysm, direct observation by open surgery is important when the relationship between the PcomA and aneurysm is not clear by neuroradiologic imaging.