Isolated third nerve palsy associated with a ruptured anterior communicating artery aneurysm

Introduction An oculomotor palsy in the setting of aneurysmal subarachnoid hemorrhage is often due to compression by a posterior communicating artery aneurysm. Anterior communicating artery (ACOM) aneurysms may produce ophthalmologic symptoms of the anterior visual pathways, but rarely ever lead to a 3rd nerve palsy. This report describes a rare case of an isolated oculomotor palsy in a patient who experienced subarachnoid hemorrhage from an ACOM aneurysm. Clinical Presentation: A 46-year-old male presented to the emergency department with headache, emesis, and an isolated left third nerve palsy - the remainder of his exam was normal. A head CT showed diffuse subarachnoid hemorrhage that was later attributed to an ACOM aneurysm as determined by angiography. Intervention Due to the configuration of the aneurysm, it was not deemed treatable by endovascular means. Following a successful clipping, the patient experienced a delayed, transient, monocular visual loss. Upon follow-up, his oculomotor palsy had completely resolved. Conclusion In very rare circumstances, an ACOM aneurysm may produce an isolated third nerve palsy. The etiology of the palsy is likely related to clot formation and/or irritating blood products.