What is the Risk of Intracranial Aneurysm with Isolated CN III Palsy?
The key issue to address for a patient presenting with CN III palsy is whether or not the palsy is caused by an intracranial aneurysm. Several recent studies have clarified the natural history of unruptured intracranial aneurysms: the 5-year risk of rupture is highly variable (between 0% and 50% per year), and depends on size and location of the aneurysm. The aneurysms with the highest rates of rupture (posterior communicating and basilar tip aneurysms) are also the aneurysms most likely to cause an isolated CN III palsy; these posterior circulation aneurysms have a rate of rupture between 2.5% and 50%, depending upon the size of the aneurysm (23). In addition, cranial nerve palsy from an aneurysm likely reflects an acute change (hemorrhage or expansion) in the aneurysm; these aneurysms may have a higher risk of rupture. When intracranial aneurysms rupture, the subsequent mortality and morbidity are extremely high. A large percentage of patients die from the initial rupture, and the re
