Acute Isolated Sixth Nerve Palsy Caused by Unruptured Intradural Saccular Aneurysm

Background: Unruptured intracranial aneurysms that cause isolated sixth nerve palsies are usually located extradurally in the cavernous sinus or intradurally as part of fusiform enlargement of the parent artery. Intradural saccular aneurysms of the vertebrobasilar circulation are a rare but life-threatening cause of isolated sixth nerve palsy. We provide documentation of 2 such cases. Methods: Case records of the Neuro-ophthalmology Clinics at the University of Michigan. Results: A 56-year-old woman with an arteriosclerotic risk profile reported new diplopia and had an isolated left sixth nerve palsy caused by an unruptured saccular aneurysm of the anterior inferior cerebellar artery. It was successfully coiled, and the sixth nerve palsy markedly improved. A 62-year-old woman with an arteriosclerotic risk profile and new diplopia had an isolated right sixth nerve palsy caused by a large unruptured vertebral artery aneurysm. It was coiled and later stented and recoiled. These procedures isolated the aneurysm and relieved the sixth nerve palsy.; ; Conclusions: Isolated sixth nerve palsies in these 2 older adult patients with arteriosclerotic risk profiles were caused by unruptured intradural vertebrobasilar aneurysms. This report adds documentation to a rare phenomenon that must be taken into consideration in deciding whether brain imaging is needed in isolated sixth nerve palsy.